Jadzia is probably my favorite female character in all of Trek. All her qualities that were already mentioned above made her a very likable and believable character.
I think she was the best female character on DS9. I know so many people really love Kira, but I just couldn't stand her. My friend told me I was being too harsh on her since she did have to live with the Cardassian occupation, but to me she always came off as whiny and annoying and I couldn't get past that.
That's why I love Jadzia and even though I knew she would die (a friend accidently spoiled it when we were talking about DS9 and I said I really liked Dax and he's like "which one?") but I think everything about her, except that BS death she got was fantastic.