Jadzia. Not Jadzia Dax, but Jadzia the host.
We know almost nothing of who Jadzia is and what unique traits she contributed to the symbiont. Ezri had a much more fully developed personality in one year than Jadzia did in six.
Agreed. After watching the series again, I realized that Jadzia wasn't as great a character as I thought. I still like her but I wish we got to know more about her. What was her full name? Did she have a family? I think I liked that aspect of Ezri the most in that we learned how the host and the symbiont really do need to work with each other to get through life and how hard that is.