It close for me between TNG and DS9 but TNG wins by a hair. DS9 a bit more consistent with the 3 worse season of DS9 being better then the 3 worse seasons of TNG but I prefer the best 4 TNG seasons over the best 4 DS9 seasons. I going to give the edge to peak over consistency especially since while DS9 did not have entire seasons I disliked as much as entire seasons of TNG there was still some extremely painful to watch episodes sprinkle into each season of DS9.
I know am going to get attacked on this one but I enjoyed discovery for most part. Does it really feel like star trek no but at least it kept me entertained.
As for enterprise truthfully I just really really enjoyed season 3. Throw that season out and it would fall way below TOS. TOS is tough one to place. There are certain episode I absolutely love The Menagerie, Balance of Terror, The City on the Edge of Forever, Trouble with Tribbles but most the other episodes just did not age well for me and found myself having a hard time concentrating long enough to get through a number of episodes.
Finally there Picard and Voyager. Picard I found absolutely horrible and not decided yet if I even attempt to watch season 2 hoping it get better or don't risk putting me through the torture of watching another season like the first. I mean TNG season one was probably the most painful season of star trek I watched till PICARD and it ended up being my favorite star trek show ever so there hope but I still not liking those odds.
As for Voyager I tried I really tried but I have not successfully made it through. I stopped somewhere in season 3. I mean what I did watch was better then Picard so there that but Picard was 10 episodes, I was already over 50 episodes into Voyager and it was still not getting better for me and I just could not take any more.