I completely agree that Deep Space Nine deserved a movie.
Whilst 'What You Leave Behind' did wrap things up nicely, there were any number of plot points that could have be revisited.
Given the rich story of the show and strong ensemble cast, then I believe that DS9 would have been the best choice for a new series to go to the silver screen. VOY certainly didn't carry the same gravitas as DS9, and I believe that the poor finale to VOY left a bad taste amongst both dedicated fans and casual viewers alike.
However, regardless of which series carried forward as a movie, I do not believe it would have resulted in commercial success.
To a previous poster saying that Nemesis 'torpedoed the franchise' isn't fair. I think the franchise had been in trouble for several years prior to this point.
I quite liked Nemesis, and whilst it pains me to say this, I don't think any movie set in the 24th century era would have succeded. Many reviewers, including mainstream reviewers, seemed to regard the TNG era movie format as somewhat tired and old. Based off the poor ticket sales for this movie, then this appears to have been a sentiment held by most of the viewing public as well.