As the Strawhats go, I really only don't like Nami.... the rest all have their good (and usually hilarious) points for me.
As other characters go, I hate Aokiji and Akainu.... Aokiji cuz he's a smug bastard who's all 'I control your life, just know that if it weren't for me, you'd be dead', and Akainu cuz he's just an evil prick.