I didn't love the character, but warmed up to her towards the end. It wasn't ideal how her character was created. In terms of Sisko warming up to her, I think it was perfectly realistic that he did so so fast. When Jadzia first came aboard the station, she had recently been joined, and he warmed up to her fairly fast. She even warned him that not all relationships from a former host survive a transfer. This was Sisko's 3rd Dax, and 2nd time he had to adjust to a permanent change.
As for Neelix, I still dislike Neelix. Not that fond of Joe (The Doctor) either. Don't think she's that bad compared to Neelix.