UPDATE: S3 Update parts are updated as of 3/29/2013
These are only junglers that you would probably see often, I am not including junglers that would be seen as a troll
Against any kind of jungler you can start with Boots
Against Rammus there should be no problem for you as Udyr. Udyr can easily steal Rammus's red before he gets there and by the time you start on red already, he should be starting his wraiths. Rammus does not have a very strong jungle speed and thus he cannot counter jungle you back. He is only feared for his ganks and if you set him behind, then he can't gank and if he does and failz, he can no longer tank any to you. When he does gank however it is really strong even without the need of red buff.
S3 Update: Rammus cannot really fight you because you do magic damage with phoenix and you yourself are pretty tanky.
Nerfs against him were too stronk, jungle became much harder for him. Basically no one uses him anymore
S3 Update: Same as above
Faster jungle and teh ability to fear and drain you makes him alot better than he was before. Silence is OP too.
S3 Update: He will still be afraid of you because you will do more damage than he can drain early on and at all points of the game you can stun him once you have bear stance which will stop his drain.
Skarner still has a decent jungle, and it probably requires you to have a really strong leash for you to fight against a skarner. Sometimes you might be able to kill red before skarner comes. His level 6 ganking potentially makes him much better than udyr later in the game.
Be careful of trying to counterjungle him since he is as fast as udyr and can slow you infinitely if you are caught in his jungle.
S3 Update: Honestly hes not seeing much use now. His jungling got nerfed a little and his ult got nerfed to the point that its not as strong anymore. You are way stronger than him in duels especially after the buffs now.
A red starting champ that you should beat usually. His jungling isn't that fast and your routes open up alot especially when he level 2 ganks, basically he level 2 ganks which he should usually do and you basically deny him his jungle. If you know he and his team invaded your jungle, you can jack his red easily after blue and prob steal some wraiths if he tries to level 2 gank after invading.
Be careful of fighting him 1v1 if you guys meet in the jungle especially if he has red because no one can beat a lee early on 1v1. He also has the ability to counterjungle you back if the lee sin is good and knows what he is doing.
S3 update: He got nerfed too much to the point he isn't that strong anymore. He can still do alot of damage but nothing you can't handle and you will most likely still outtrade if played right especially after the buffs.
Meh still not that great of a pick, but its gotten slightly better. Can't really do anything against him in a 1v1 situation. Probably can still steal off of.
S3 Update: Still sux
He can go straight from blue to red and do a level 3 gank, so be careful. It might be dangerous if you are caught in his jungle due to his knockup and his samplings can be used as a sort of ward for his teammates. Also the wraith route to blue has been taken alot less frequently including myself.
S3 Update: He is ok right now in the jungle. He is a strong ganker, however he is more of a cc bot than doing damage. You can outdamage him at all points in the game.
He gets pretty damn low in the jungle, but he still clears the jungle super fast. Be careful if your counterjungling, but you should have more pressure in a 1v1 compared to him since mundo is the weakest in the early game.
S3 Update: He is strong late game. However his early game is weak and is not a common pick at all anymore. Udyr can beat him early to mid game and can perform his role late game like mundo does. He has no cc other than skillshot cleavers for slow.
She is basically on par with udyr early on. She has more route options due to her not needing to rely on mana whereas Udyr is pretty reliant early on to do his jungle or counter jungle. A shyvana can duel equally with udyr and possibly slightly better due to udyr needing phoenix procs while shyvana's skill have constant damage and low cds. You have cc compared to her which usually forces her to run exhaust. And early duel with a shyvana should not be recommended because her exhaust would cause you to lose the fight. Since she is similar to mundo, it is suggested take shyvana like she is mundo.
S3 Update: She is pretty weak right now in the current jungle. She has no cc in a jungle meta where it is gank reliant.
A good shaco will know what to do and will absolutely wreck either your jungle or the enemy lanes. Be careful around him. He can stack mass boxes in your jungle. Take your buffs extremely fast and suprise you when you least expect it.
S3 Update: I hate him so much still.
Nocturne clears quite fast in the new jungle and his fear and damage is stronger than Udyrs. Be careful if you get caught.
S3 Update: His fear is annoying if he gets the proc off and can be quite threatening if hes a round a teammate. You are naturally tankier in 1v1 than him and do more damage to him due to your base damage from phoenix.
He has a decent jungle speed but still not that great. His early jungle is pretty weak and relies on blue pretty hard. His slow is rather annoying and he can orange your stun so don't fight him too long if you're in his jungle. He can't fight you in the jungle early on and even later on.
S3 Update: No one really uses him anymore since he sucks rite now still.
You can steal red, but don't try to fight him 1v1, because he is way too tanky for you to kill even with red. the attack speed debuff he has also makes it harder for phoenix procs.
S3 Update: He is not that common since his jungling is extremely slow and cannot fight against you at all.
He has a slow jungle and mainly relies on ganking which makes counterjungling him easy. You screw him up the most if you can take most of his blue away from him. You can totally fight him and kick his ass. Careful of his cc though if his team catches you.
S3 Update: He is currently Big 5 jungler but nothing you can't handle since most of his potential is from ganking rather than dueling which you excel at.
She can be a red jungler, but she like every other jungler, they can chose to go blue if they wanted. I generally check the wraiths to see if they started red OR which way the lanes walk from to see which part of the jungle they leashed from. Knowing where your oppoennt starts gives you a huge advantage. Riven has a somewhat slow jungle too and if you want to fight her wait for her to use all her Q's if you can before fighting her.
S3 Update: Haven't seen any at all in a long time so I would assume she wouldn't really beat udyr in fights.
Amumu is a pretty decent to fast jungler and is basically one of the strongest if not the strongest jungler currently due to the new items and utility he brings. He also does quite some damage. So be careful of him especially if he has bandage.
S3 Update: Still good after nerfs, be careful not to get caught in his cc.
Decent jungle. You should be able to steal from him easily if his red isn't warded or check on you early. He's known for his ganks so try to delay his jungle if you can so he doesnn't get many ganks off. Try to deny him or his ganks will be completely brutal to your team. If you can't counterjungle him, try to countergank lanes he will gank because his cc is crazy in fights. If you are caught by a nautilus with an enemy lane nearby, he can easily cc you long enough to the point the enemy lane can catch up to you and rape you.
S3 Update: haven't really seen almost any lately due to his weak jungle clears which makes him really easy to kill since he gets pretty low in the jungle. He however makes up for it with strong ganks still.
Has a somewhat slow still jungle, he cannot duel but has a taunt. He generally starts red which would make it hard to counterjungle normally. You can fight him at most points of the game in a duel but watch out when his teammates are near. Note however that once he is 6 he can gank from anywhere from the map.
S3 Update: Not that common at all. He is tanky but doesn't really do damage. You can't really kill him unless you hit him for a long time but hes nothing scary by himself.
STILL BAD. Easy. Horrible jungler right now. Needs lots farm. Needz kills. Can't fight early in jungle
S3 Update: LOL ^
Difficulty: very easy
He has a good clear speed in the new S3 jungle and has a dodge to not get hit by your autoattacks. He is a hypercarry and not a tank so he doesn't really fit as a jungler in a team right now.
S3 Update: He is a pretty good jungler, he is not that bad unless he becomes really fed especially after 6. He doesn't really fulfill the current jungle role as being tanky since he is a hypercarry bruiser.
Nunu is a strong counterjungler due to his consume and smite which can take down any neutral buff, dragon, and baron better than any other other than possibly jungler with the small exception being chogath. Beware when he tries to steal a buff from you or especially baron or dragon because he can basically do a double smite in which you have no way to prevent unless your teammates gets rid of him. Fighting him might be a bit difficult because he has a slow which makes Udyr easily kitable as well as a speed buff of his own, making it impossible for udyr to catch him. It is possible to counterjungle him, however if you are caught, his slow and AS steroid and movement speed buff with red can make it hell for you to get away and making it easy for his teammates to reach you. He is basically like a counter to you with infinite slow.
S3 update: The nerfs to him made him not as hard to catch which made his pick rate to drop immensely. He is still probably incredibly annoying to fight against due to his slows.
New jungle kinda nerfed him down a bit compared to other junglers. He is still a threat if you are caught by him.
S3 Update: Don't listen to above idk wut im talking about lol. Xin is currently one of the strongest junglers in the current jungle. His ganks are strong, and decent cc. He is also a strong duelist which can probably fight on par with you depending on situations.
He is a very strong jungler right now. Support tank. Provides more utility than you and has innate tankyness from his ult. He also does true damage. A knockup(if you can land it) and a silence. His vorpal spikes also helps increase his clears and has innate sustain from killing the jungle. He is also pretty fast too.
S3 Update: still a good jungler. He is more of a lategame tank. He provides good utility for the team but not a big threat to you.
Difficulty: Medium - Hard
She got nerfed soo hard that she wont even be picked anymore in mid lane.
S3 update: She is ok right now but better in mid lane since she got rebuffed.
Personally in the new S3 jungle, hecarims just not as good because he never really had a good clear speed and he is not that great at killing buffs either especially since they buffed the hp on the big wolves/wraiths and buff monsters.
S3 Update: His w got nerfed alot, however is still decent in the jungle but not as strong as he used to be. O btw don't listen to me for the above lol.
da nerfs don't allow him to be played. Probably a red starter since he is manaless
S3 Update: I forgot he existed lol
Difficulty: Easy- Medium
Hmm, he is ok in the jungle but he is not that fast and is quite weak early since he relies alot on levels. He seems to be better off in a solo lane however his ganks are quite strong since his Q can do an initial massive amount of damage and he has a gap closer jump that can catch your lanes in suprise. Possibly able to be counterjungled easily. New S3 items gave him a huge buff and hes basically OP everywhere now. He does win in 1v1 matchup because hes basically the king at that. So be careful.
S3 Update: meh he is ok in the jungle right now. He isn't really that scary.
S3 Update: Her early game is pretty strong. Don't let get multiple autoattacks because it can hurt in a duel. She has 2 knockups with 1 of them being unavoidable which can make it hard since her ganks are incredibly strong with her ult. Somewhat of a scary jungler but nothing that you yourself should be afraid of....maybe your lanemates.
Difficulty: Medium - Hard
Its impossible, just afk cuz you know you've lost
S3 Update: Riot cudnt delete