Silver is my favourite, followed by Gary. Those two were ones you liked to hate and beat up, haha, and Silver had some character development going there as well.
I liked Belle and Cheren as well, just not as much (a bit too exaggerated imo in some aspects of personality, although I wouldn't mind seeing how they are in B2W2 in english... and that game's rival too). Barry was amusing and had a good battle theme but besides that not much else, N I plain dislike, Wally had a neat concept but was hardly seen (disappeared for over half a game only to turn up in Victory Road), and RSE's main rivals were the worst imo. Always giving you presents despite losing and then give up halfway through. Some rival!