This was a pretty tough choice between TNG and DS9 for me. Ultimately I had to go with TNG as I found I liked more of the characters on that show and many of the characters I liked on DS9 came from TNG anyway (Worf, Miles O'Brian). I prefer Picard to Sisko, although Sisko did end up being a fairly interesting character by the end. I just felt Jonathan Patrick Stewart was a much better actor than Avery Brooks (IMO of course).
Also, although TNG didn't have a contiguous storyline, and I did really enjoy the Dominion war, I suppose I enjoyed the entirety of the TNG series more than the entirety of DS9. I mean, DS9 before the Dominion war was every-bit the Star Trek formula for episodes; the fact that they stayed in one place did allow them to build a storyline though (if slowly). The Dominion war itself was interesting but somewhat derivative of Babylon 5 (which I enjoyed more than any Trek series). And ultimately I never really liked Sisko as a chosen of the Prophets: I would rather that have been another character (although I have no idea who). I just felt that at the end of the series, it would have been much more compelling to see Sisko versus Gul Ducat without each of them being tied to some strange quasi-deities. Their original personalities were much more interesting IMO.