I don't really hate any of the main characters, but if I had to choose one I have the least liking of ... I'd say Ezri. She had some great storylines in her only season, but she just didn't have the same impact for me as Jadzia. As far as recurring characters, I would have to say Gowron. I never cared for him on TNG and was happy to see him go on DS9.
I've come to appreciate the influence Ezri's presence had on some of the other characters, especially Worf. But I agree, on her own, ho hum.
And OMG, Gowron's death was what, 10 or so years in the making? I still remember watching that episode on my crummy, staticy, tiny dorm room television, and almost falling off my loft I was so stoked by it. Fortunately my roommate was not there at the time...