I'll probably end up voting for Jadzia since she's my favourite DS9 character, but you never know, and it's too early for me to vote. I've only seen the first two episodes of season 7, and Ezri has been my favourite part of both. So far I like her a lot (but for different reasons than Jadzia) and am curious to see how the other characters play off her.
She irritated me a little when she started talking all hyperactively about how freaked out she was about being joined and the circumstances that lead to her joining, but it was a very minor annoyance. Overall, I'm digging how vulnerable and honest about her insecurities she is. It's a refreshing contrast from Jadzia's unshakable confidence (not that I didn't appreciate this about her).
It's two episodes in a row now that the writers have used people learning of her existence for the first time as a cliffhanger, and while it's really uncreative of them to repeat the same tactic twice, I gotta admit that it's a hell of an effective trick. I'm really excited to see what happens in the third episode of the season, which I believe is very much about her and how the others intially react to her presence on the station.