Voyager and DS9 were always superior to me than TNG. TNG hasn't aged well where I can still watch the other. But Voyager and DS9 do have quite a rough go of it for some seasons - where TNG had a lot of rough seasons and episodes before hitting their stride in the last few seasons.
Voyager's first season had a great premise (and not just ripping off the Lost in Space cliche) with some awful episodes (Amelia Airheart) and some outright stupid new agey ideas. Kess hit her stride in season 3 just when they got rid of her, and as much as I liked 7, there were just way too many episodes of her.
DS9 started off incredible, though Kira was not believable except in the pilot. It started going downhill after they got rid of Keiko O'Brien and really faltered by bringing Worf into the series. This completely ruined the chemistry the cast had built and the writers forgot that, at least on paper, Miles and Worf were supposed to be really good friends - at least off camera (O'Brien helped to organize and attended his pain stick ceremony). Things got back onstride with the war/invasion of shapeshifters, which affected the mood of TNG movies and even leaked out to Voyager as they learned the Maquis were no more. Around this time Avery Brooks story had mostly finished and he became more of a director then the central character - an interesting premise where the main character becomes the supporting character for the ensemble. The final season was lousy except for the new character.
My favourite of all time though is the TAS.