This is by no means a complete list due to the changes in the jungle. The champions who can jungle have changed, but I will cover those which I believe are still a threat and the ones you can easily counter.
Is any easy opponent to counter jungle because of his slow clear. You can start at his wraiths and still get your blue. By doing this you've set him back quite a bit in XP and you've made it more difficult for him to have any early game presence. But from the time he reaches Level 6 and into the later stages of the game he is going to be difficult to deal with in team fights. His jungle clear is now pretty fast and you should be more concerned about getting your ganks and CS early game so that you have most of your build by mid to late game.
Eve is an interesting pick for the new jungle and because of the changes to the jungle she gets hit hard by the neutral camps. She is an easy counter jungle at wraiths and if you ward you may even be able to catch her off guard and gank her in her own jungle at low health. As long as your team is buying pink wards she is not a huge threat when she comes to gank, but if your team isn't warding properly she can become a huge problem. In a 1v1 you're going to win nearly every time so don't be afraid to jump her in the jungle.
Although he gets banned a lot, a jungle Malphite has an extremely slow clear which should give you a great counter jungling advantage. He typically starts at wolves or blue and so you can have his wraiths. He's another champion that doesn't have the best ganks until Level 6, but if your team is caught off guard his slow coupled with an ADC is deadly. As the game goes on Malphite becomes tankier and a bigger issue in team fights because of his ultimate and burst. If you can survive his ultimate and initial burst while targeting the ADC or APC, with decent coordination you should win every team fight.
Is not a threat in the jungle, but I wouldn't counter him either. His clear speed is totally random with his Q it could be a one shot thing or he can get stuck on wolves for 10 seconds. He's really squishy so unless he really gets the jump on you or your team I wouldn't be too worried. In teams fights I would still focus the Carries, but Yi is another viable target. His damage is very bursty and once he's hit his Q his damage is pretty much minimal for the next 7 - 10 seconds.
Just like Malphite, Nautilus has an extremely slow clear. He's easily counter jungled, but is very tanky with his shield. Be careful of running into him 1v1 in the jungle. As long as your team has wards he's not a threat for ganks and even into late game you just have to be careful of him initiating with a pull in team fights.
Vi is an interesting champ and can have a really strong late game with her engage, but her early jungle game is just plain bad. She has slow to average clear times depending on the player skill, but either way you should be countering her off the bat. Because she starts Blue you should rush Enemy Red and ward the bush at Wraiths. If it's safe take Big Wraith and leave 3 little ones, then take her Red Buff and Big Golem and do an early gank on whichever lane is near her Red. Now that you have the buff timer this gives you an opportunity to really set her back and potentially secure a First Blood for your Top/Bot lane and continue to steal her Red.
Kha'Zix is a very skill based opponent. Some players are really good and others, not so much. I would suggest warding his wraiths in the beginning of the game to see where he's at health wise after he's finished Blue/Wolves. If he's low then he can probably be countered pretty easily, but if he's got 75% or more HP then he's going to be an early game threat. You could start at his wraiths to try to set him back, but make sure to bring a team mate with you. Against Kha'Zix the best thing you can do is rush Level 6 and make sure your team is warding. Like I said before, he's very skill based so in a team fight he could be very dangerous or just an annoyance. In a 1v1 you're not going to win because he can just Ult and disappear or even jump away.
In my opinion is not a good jungler, but he's very annoying when played properly. He's fast and therefore will be in your jungle a lot. Make sure that you're warding your own jungle to prevent him from countering. His ganks aren't very strong unless his target is low on health. In a 1v1 you might win, but I wouldn't leave it up to chance. In team fights you shouldn't ignore him, but he shouldn't be your first target either. Even if you kill everyone but Rammus, you will get a tower or inhibitor out of the fight.
Shaco is a menace in the early stages of the game, he can gank at Level 2 if he wants. You can't counter him either because he'll put a box down at all of his camps. Fortunately though, if your team can deny him early ganks you will shut him down for the rest of the game. Shaco is a champion that doesn't scale well into late game like other champions and therefore he should not be a threat unless he gets his ganks. Like Rammus, even if he gets away he's not going to stop 4 or 5 of you from steam rolling a tower and inhib.
If you play blind pick and you get matched up against another Warwick it comes down to who's better and smarter. If you want the upper hand you should try to take his wraiths off the bat, but to keep him from doing the same have someone on your team guard your wraiths. You'll have a lot of lane security until Level 6 because you both can't really gank until then. In a 1v1 it's going to come down to who built a Wit's End first, after that it could go either way. In team fights a lot of times you will get focused and blown up, but I'd recommend focusing their ADC or APC because after your Ultimate your damage is limited and if you've killed their ADC or APC then they're probably in trouble.
Cho is can be a very scary jungler for you and your team. Although his clears are slow early on he has a mixture of damage that is hard to counter early on. His rupture and silence can put you out of the game for quite a while and you won't be able to get a Q off to heal yourself. I wouldn't recommend going up against him 1v1 in the jungle, especially if he has stacks built up. In a team fight he's a big threat because of his CC, but if you've learned anything from this guide, taking out the ADC and APC will give you a better opportunity to take out a beast like Cho.
Although you don't see a Darius in the jungle too often, it still happens. His clear times are slow early on and then pretty average as the game progresses. You can probably get away with some counter jungling, but only if you've warded their jungle. Darius hits really hard with all of his abilities and so I would not recommend fighting him in a 1v1. Finally, there's something my friends and I like to call "The Darius Factor." Basically The Darius Factor states that no matter how hard you're losing (as Darius) you're team can still pull through in late game because of the damage he puts out even with a bare bones build. The refresh on his R is a killer in team fights and is obviously something that should be avoided. Even when you think you have Darius beat you shouldn't count him out.
Is one of the fastest clearing jungles if played correctly. He's not someone to be countered and he's certainly not someone to 1v1. Make sure to ward your jungle because it is not uncommon that he will try to counter you. He's going to be a pain the entire game and the best thing you can do to shut him and his team down is to race to Level 6 and start ganking. Helping you team get fed is what will shut him and his team down. Don't ever focus him down in a team fight because they're ADC and APC will destroy your team while you try to kill him.
Is a scary opponent for a few reasons. Since the changes to the jungle in Season 3, Fiddle in the jungle is extremely viable and built for Warwick and Fiddle. His lifesteal means that he's going to have health almost the entire time. Even though he's squishy you should still be afraid because his fear will CC you long enough to kill you before you even get a Q off. His pre-6 ganks aren't too strong, but if your team isn't warding they're going to find themselves dead. Once he's Level 6 your team HAS to be warding every bush because he will flash and crow storm everything and everyone will be dead. In a team fight he's going to CC really hard because his fear lasts for roughly 3 seconds in the late stages which is long enough for a 5v5 fight to quick become a 5v4. His ultimate is dangerous when your team is low so make sure everyone is healed up before you initiate.
Although Jax has a pretty slow clear time, his ganks and late game are what make him scary. You can't 1v1 him because he is a hard counter to melee champs. If your team is able to keep him from ganking then you're probably going to be fine for late game. If not then he becomes a huge issue because he can easily tank towers and destroy your team in a fight.
Lee Sin is an annoyance to you from the start. He's going to counter you very aggressively and you should be prepared for that with wards. Another option would be to just counter him as well. His ganks can be some what scary, but as long as he doesn't get too many he isn't a real issue. He's a hard opponent because he limits your CS in the jungle and late game he can be a threat, but he's mostly good for running away in a team fight. But he's better at catching stragglers so always stay together.
Maoki is just like Lee Sin, he's an annoyance and is probably going to counter jungle. The only difference is that his ganks are really powerful. He has a lot of CC and can really shut down your lanes. In a 1v1 you might win, but I would be careful. The best thing you can do to defend yourself from Maoki is to ward your jungle and his wraiths so that you can make some attempts to counter jungle him. Late game he's still some what of a threat, but your team just has to be careful of his ult and you'll survive.
Nocturne is scary to play against. He's not a huge counter jungle presence, but his lane presence is what makes him scary. A good Nocturne can easily shut down your top and mid lanes and make it hell for your bottom lane to win. It's best for you and your team to play more passively against a team with Nocturne because even if he hits you with an ult and you're close enough to a tower, you might escape or get him killed by the tower. In team fights Nocturne has a lot of CC and it makes it difficult for your team, but shutting down the ADC and APC are your number one goals.
Nunu is another one who's known to counter jungle pretty hard. He's a menace in lane because of his slow and he'll flash ult an entire team. You may be able to take him on in a 1v1 early on, but I wouldn't count on it later in the game. The best thing you and your team can do is ward and ward bushes. His ult is probably the most dangerous thing about him. A good Nunu is scary to deal with during a gank because he'll consume a minion to save himself.
Olaf has a pretty quick jungle time and he can be a presence in lane relatively early. He's dangerous because he deals true damage and it can only be countered by stacking health. If he's really aggressive he may try to counter jungle, but I'd imagine he'd spend more time harassing lanes if he was aggressive. Running into him 1v1 won't end well so you should try to avoid it. In the later stages of the game he will still be a problem, but hopefully your team was smart enough to build some items that counter him.
Has an average clear time, but what makes him scary is how tanky he is and his ultimate. He won't be in your jungle much, but he can easily counter gank you with his ultimate. In team fights he can definitely be an issue as well, but should not be your teams focus.
Rengar does not have a fast clear time, but what he is good at is being overpowered. He'll jump your lanes and blow them up before they even knew what hit them. I always ward enemy wraiths when I face Rengar because you'll have some idea of where he is throughout the game. It may just be a bug, but you can use your R to jump Rengar and you will stay on him even if he goes invisible. It's a nifty trick for team fights or catching him out of position.
Shyv is has a pretty fast clear time which makes her a presence in lane early on. She's also one of the best duelists so you probably shouldn't try and fight her 1v1. Seeing as she starts Red you could attempt to steal her blue, but she may also try to counter you by taking your Red. Be sure to have your bottom lane guard Red whenever you're against her. Her ganks become stronger as the game progresses so you need to do your best to get to Level 6 and start ganking as well. In team fights she's kind of a threat depending on the way she builds. The more offensive her build is the scarier she will be. If she goes the tankier route her damage is slightly limited, but you should prioritize her AFTER you kill the ADC and APC since she's usually slow to get away.
Skarner has a very fast clear in the new jungle and he's a big threat to your jungle. You need to ward against Skarner otherwise he will shut you and your team down. He's very tanky and I would advice not fighting him 1v1. In the team fight scenarios it is best to keep away from him during the poking stages because if he carries you or one of your teammates away the fight just turned into a 4v5 and you probably lost.
Trundle is an interesting jungler because of his abilities. He can be somewhat tanky, but he's better at juking and keep you and your team off of him. He's not really one to counter jungle, but I wouldn't counter jungle him because you might get caught and stuck. His ganks can be strong if he uses his abilities to his advantage, otherwise they're average at best. In team fights he is only a nuisance so I wouldn't stress killing him first.
Is just like Maoki and Lee Sin, he's going to harass you and your team all game. He's an aggressive counter jungler and you should do your best to ward against him. His ganks aren't terribly strong early game, but he can become very dangerous as the game progresses. In a team fight he's one of the last champions you should focus and like Rammus will be one of the first ones to run away because of his speed.
Xin has a good clear time and has very dangerous ganks. If Xin gets fed it's practically game over. The best thing you can do is try to slow him by starting at his wraiths, but otherwise warding if only going to help you and your team prevent him from ganking. In a team fight he can use his ultimate to knock you back to save his team or he can use it to knock you into a turret. Positioning is key when fighting Xin and you should be careful not to get between him and a tower.