At the time of airing the answer would be Ezri. I was active in fan communities way back then when the internet was new (usenet anyone?) and everyone was pretty pissed that Jadzi was replaced by her. Most peoole figured they would just go down to one female lead, that it woukd be too tough to bring in someone new the last season. Ezri has only gained respect among fans in hindsight (myself included)
Yeah, I imagine their decision to replace Jadzia caused quite an uproar among the fans. But what else could they do? They couldn't have just one
regular female character. However, they didn't necessarily have to have another Dax. They could have just added a completely new character. I think that's part of why people resent Ezri. She wasn't just a new character; she was a new Dax
, and the viewer just had to accept it. It was a lot to expect from fans.
I'm personally not a fan of Ezri, but not because she replaced Jadzia. She's just too bubbly and perky, and I'm usually not crazy about those kinds of characters. But that's just me; I realize a lot of people do like her, and I can understand why.