Udyr's arguably the best jungle in LoL. Abusing the combination of turtle and phoenix stance for a nice shield and DoT is pretty damn good. Especially when you throw in a sheen passive. It'll always have your enemies raging like crazy, which makes things even better. And another thing, if you're playing against someone like Malzahar or Soraka who has a silence, more likely than not, you want to pick up quicksilver sash in place of sunfire.

note: this says to drop wriggle's and greaves for sunfire and thirster, but you don't. You sell HoG for Sunfire Cape, and then Wriggle's for BloodThirster. Just wanted to let you guys know.

Udyr's incredibly easy to use, and is pretty noob friendly. You just use turtle then pheonix when they come off cd. You won't take much dmg, but you deal lots of it. Oh, and switch to Tiger when both phoenix and turtle are on cd. So, your skill "combo" is Turtle -> Phoenix -> Tiger then repeat. Use bear to initiate fights when you gank.

Pros
1.) He's incredibly easy to use.
2.) You take little to no damage when farming creeps in the jungle.
3.) Turtle Stance makes you a tank, in addition to a melee carry/dps.
Cons
1.) You're that good laning.
2.) Your build is kinda exspensive, and requires lots of cs/kills/assists to obtain.
3.) You're completely useless when silenced.