Deep Space Nine, hands down. But then again, every single TNG character would have become so much more in the hands of the DS9 writers.
Funny, since most of DS9's writers came from TNG...
In the DS9 companion there's an anecdote about how Ronald D. Moore joined the writing staff of DS9. He was actually all eager to join Voyager since he wanted to try being on the staff of a show from the beginning. When asked to join DS9 he said, "I donwanna" but I think it was either Michael Piller or Jeri Taylor who urged him to do so saying "You'll learn a lot working for Ira Stephen Behr." And I would say that he did. Basically, my point is that people grow and change.
Another point I'd make, and I apologize for the gross over-simplification, is that TNG had a nice balance of science fiction and character development. It tended to be the writers who wrote more of the character-based stories went to DS9 (Ronald D. Moore, Rene Echevarria, Hans Beimler), while the more high-concept writers went to VOY (Joe Menosky, Brannon Braga). I think that in such a marriage of styles the character-based writers tend to be more creatively successful after the divorce.