User blog comment:AntiZig/Jungling Strategies for various champs/@comment-3360527-20110406132134

Leveling speed will also be swayed by successful/failled ganks as well as failing lanes that the jungler has to leave his route to cover because they keep dieing or having to recall. The best/fastest junglers are ones that can keep a decent sustained route as well as gank well (assuming their lane teammates aren't pushing their lanes). Udyr, Cho, Nunu, Nocturne, Shaco, and Shen are pretty effective at ganking before level 6. Olaf, Rammus, Amumu are pretty good at it as well. The good post-6 junglers are fiddle, akali, WW are great once they get their ult.

The next big piece of the puzzle is if or how good the other team is at counter-jungling. Shutting out a jungler of his blue will REALLY hurt his early and mid game.