I've always liked them, but Sandslash, Absol, and Delphox are Pokémon that I've really begun to appreciate a lot more recently.
As for Pokémon that I outright disliked, I used to think Cramorant looked really stupid. After giving it a chance in one playthrough, I found that it was really fun to use due to its ability. It was also surprisingly strong and I could always count on it on the (admittedly rare) occasion that I was in trouble. The ugly-cute design also kind of grew on me.