Hard one. Either Caitlin due to her battle frontier apperances. Shauntaul, coz she writes stories and has an awesome team or grimsley coz I love dark types and he looks epic. The only thing they could do to his team to make it better would be to stick an absol on it.
My List of Favorites (From BEST TO least):
I LOVE LOVE LOVE Psychic but I love Gothitelle EVEN more! I also like Sigi.
Easy, fun, and I love Jellicent and Chandelure!
Dude, he is weird. He just irks me. I do love Scrafty however.
I don't necessarily hate him, I just found that he was difficult and stubborn. I also don't like, in fact I Hate Throw.
Caitlin because to me she's the most memorable Elite Four trainers in B/W. I don't even remember what the rest looked like... But Caitlin is rather funny since she acts like princess. But this time she at least battled herself and not let her butler to do the battling
Caitlyn and Grimsley most probably. It's been forever since I beat them on Black (2 years?) and I'm just now coming up to them again for a second round in White. I'll see how my opinion changes once I rematch them.
Grimsley because he was the easiest to defeat for me by spamming Emboar's brick break lol
But other than that, I would say Caitlin because she was so dedicated to the Elite Four that she slept there waiting for challengers.