Since I gave more info to Louise...I'll tell my opinions about the series I have watched.
Can't say anything about TOS as I have never watched it but have seen the 6 TOS movies
The Next Generation: The series was great and I loved it. Great episodes. I plan on getting the DVD box sets. TNG is my first most favorite.
Deep Space Nine: Well...I didn't watch all of season 1 and 2 as I didn't see those two seasons very interesting to me as I found those 2 seasons kinda boring (don't hurt me lol) but I did see most of season 3 and watched all of season 4, 5, 6 and 7. The series to me and to many of us, its a decent series. Great in some ways...mainly for season 5 to 7 more. Perhaps I should get the dvd box sets for this series to give season 1 and 2 another try and watch all of it, and yes, all the seasons too lol DS9 is my third favorite series.
Voyager: Voyager is my 2nd most favorite trek series. The series was great and so on. Great episodes there and there. I plan on getting the dvd box sets for this series too.
As for the TOS movies...
All TOS movies were great except that The Motion Pictures and The Voyage Home...in my opinion were decent/alright movies
I loved all 4 TNG movies. First Contact was the best TNG movie by the way...you'll enjoy that one the most.