How recurring is recurring? Garak and Nog feel like main characters even if they weren't in the credits.
Anyway, if Garak counts he's the obvious #1, so I'll leave him out:
1. Kai Winn
Might be the most realistic politician I've ever seen in a TV show, not counting the last few episodes.
2. Gul Dukat
Maybe the most realistic dictator.
I love duplicitous characters the most.
4. The Prophets
Every time they show up it's a little awesome
With Fontaine, it's not Fontaine I had a problem with, so much as everybody's obsession with him. As a brief diversion, sure, but the obsession with him wasn't well explained.