I'd love to help you some time if you want to add me on NA. My username is the same as my Boards username: Willahelm Fulber.
As for one champion, I can't really say there is simply one; each jungler has its own strengths and weaknesses, for example a lot of AP jungles (Karthus, Fiddlesticks, Casseiopeia) are really mana hungry in jungle, but have great clear times and (with the exception of fiddlesticks) pretty poor ganks unless the laner has hard cc. On the other hand, there are the ADC Jungles (Jinx, Vayne come to mind as the excellent adc jungles) who aren't really blue reliant but can easily get killed if they run into an enemy. There are the "mainstream" junglers: Udyr, XinZhao, Rengar, etc. who all have great farming and ganking potential, and then there's champions like Nautilus, Maokai, Blitzcrank, Amumu, who can gank really well on DPS lanes but can't duel really well against most other junglers.
To be honest, it is probably better to pick a champion you already know really well who can jungle (yes, a lot of supports -can- jungle, but no, not squishy supports.) and learn the mindset of a jungler from there, which is a pretty complicated thing.