TOS-TNG-DS9-Voy-Ent
I'm just going with the order that they appeared. TNG is my favorite TV show ever and what got me hooked on Trek before I discovered the original series, but I wouldn't have had it without the equally awesome original series, so I don't mind putting the original first. I love both. Trek started going downhill after TNG ended, IMO. It wasn't a rapid descent, since DS9 was very good and I enjoyed it, but it sped up with Voyager. Truth be told, I haven't seen enough of Voyager and Enterprise (particularly Enterprise) to accurately rank the two relative to one another, so I'm taking a guess with those two and could flip them if I were to watch more.