Buffy is a good one. Never warmed up to her... actually I'd say I was neutral towards her and liked her less and less as the show went on.
Angel on the other hand I hated from the start, what with his stupid caveman face,but eventually he grew on me to the point I rather liked him. Still Team Spike tho.
I considered Jack on Lost to be the main character, at least at the start, and I didn't like him. He grew on me too.
Never liked Sinclair on Babylon 5, but Sheridan was tolerable.
Don't really like Raylon on Justified.
Leslie Knope on Parks and Recreation.
I didn't like Bill from Big Love.