Definitely Neji, Konohamaru and Shikamaru. Lee has some serious taijutsu potential as well. Contrary to popular belief, Sakura has great potential as well... if only Kishi knew how to write decent female characters >.>
The only females that don't suck are Konan and Kushina. The rest are basically all stereotypes of some sort and boring.
temari, mei, hinata, tsunade and that iwa grandchild of oonoki's with the ridiculously complicated name aren't boring.
in fact, the only three boring female characters in the show are sakura, tenten, and moegi. it's true, sakura could have gone much better especially with the great start in shippuden, but at least she's a incredibly talented medical nin, not a total loss.
anyway, konohamaru has the potential to be the strongest by far, he's the only one with the potential to be naruto level.
neji can be a great fighter as well, it's a pity we didn't see much of his progress. his fight vs kidomaru was one of my favourites. it's a pity he and his team didn't get much action apart from gai.
shino is also a very intriguing and underrated character, very smart and ruthless, he's the one who is most shinobi-like out of the konoha 11 imo.
and shikamaru could be a great shinobi if he just improves his chakra pool. maybe not very powerful and deadly, but still really efffective.
although overall the most powerful is going to be Chouji. he's tapped into his potential now and is very hard to deal with in his butterfly mode.
