TNG is definitely my favorite ST series, maybe because of my age. I never really liked TOS although I loved most of the movies with that cast.
At any rate I found DS9 to be pretty boring until later in the show when the Dominion War story arc began.
Voyager was pretty good IMO but could have been better. 7of9 was definitely over used. Of course I guess that has something to do with Jeri Ryan dating Brannon Braga who's a damn writer on the show! I even heard that she was originally slated to cameo in Nemesis instead of Janeway but it was changed due to scheduling conflicts.
How in the hell would they have even written it in? Then again they didn't explain how Worf was there either so what does it matter.
As far as Enterprise goes, I've never even watched a single episode. I'll stick with my 7 TNG DVD Boxed Sets.