Here's my list:
Ezri Dax is my #1. After a long period of overall dark and intense storylines, culminating in the tragic death of Jadzia and the near-crushing, emotionally, of Sisko...the creators brought in a young and sweetly beautiful ninth host of Dax, who viewed the universe--and life--with a childlike innocence and idealism, and a romantic heart. And the best part--she was thrown into her new life, and has to gather herself together, to discover the heroine within herself. And she does.
Odo is my close second. Of all the characters, he is the one I identify with the most. His firm, uncompromising sense of Justice--his hard-boiled attitude...and his status as an outsider--all are things I admire about him, and sympathize with. And he's a secret romantic, to boot. (Funny note: I took a "What DS9 Character Are You?" survey, some time ago. Guess who it picked for me.

)
Third place--
Julian Bashir. Other than courting and winning the heart of the beautiful Ezri...he self-conciously models himself after James Bond, and has a great sense of style and charm to that effect. He's a gentlemen, and a genius--and like Odo, he finds himself an outsider--but for a much different reason.
Fourth--
Garak. Plain. Simple. Garak.
Fifth--
Luther Sloan. Many see him as a villain--understandably, as he does some pretty nasty stuff! Still, there are many fans--myself included--who see him as much more--a tragic hero, and
antihero, who proved willing and able to, quite literally, sacrifice his Life, his Fortunes...and his Sacred Honor, to do what he thought was necessary and proper to protect and defend the Federation. William Sadler played him wonderfully, conveying this sense of tragedy in moments like the ending sequence of "Inter Arma Enin Silent Leges," when he seems to have a look of sad understanding towards Bashir. (And for a brief moment...it seems like the feeling is mutual.)
Close sixth--
Quark. Arrogant, greedy, ruthless. Gotta love the guy.