1) Sisko - Obviously. He's the Emissary and one of my three favorite characters in all of Star Trek.
2) Garak - Only DS9 could have pulled off a character like Garak. Andy Robinson stole every scene he was in.
3) Kira - Kira carried the show in its early seasons; most of my favorite episodes from the first couple seasons were Kira episodes. While the Odo romance was charming, I feel Kira lost her way for the last half of the show. I still loved the character, but far too often she was defined by that "will they/won't they" romance storyline.
4) Jadzia Dax - The opposite of Kira: Jadzia got better as the show went along. I loved her ability to balance deep intellect with vibrant joy; sort of a female Einstein, in a way.
5) Vic Fontaine - I get the feeling Vic is unpopular in some parts. I don't know why because I love the guy. I love James Darren's performance, I love the songs, I love the Vegas coolness.
6) Bashir - Bashir went through a lot of phases (wide-eyed newbie, Garak-Bromance, secretive and self-loathing enhanced Bashir, Section 31, and war-weary vet), and I enjoyed them all.
7) Quark - Sure, Quark didn't really develop much over the course of the series (and some of those Ferengi comedy episodes fell flat), but Armin Shimerman owned this role and brought some much needed lightness to the series.
8) O'Brien - I love Colm Meaney. One of my favorite character actors of the past thirty years. I loved the O'Brien-Bashir bromance. But he's further down on this list because, like Quark, O'Brien didn't develop very much over the series.
9) Odo - I loved Odo in the early seasons: the outsider, the detective, the cynic. Something very different than we had seen before in Trek. But between his romance with Kira and his arc with the Founders, Odo became a bit of a bore in the later seasons. No fault of Rene Auberjonois; he was amazing.
10) Dukat - Yeah, that last season really hurt Dukat's character and dropped him to down the list, but pre-pah wraith Dukat was a spectacular villain.