Not voting, because it requires choosing one above all others.
I date back to the Stone Age, when all that existed were things like The Twilight Zone, The Outer Limits, Voyage to the Bottom of the Sea, and Lost in Space. And then Star Trek raised its head and changed the face of science fiction on television. That incarnation of Star Trek is all we had for 20 years. The later series are simply variations on the theme.
Each successive series has its own moments of excellence and pitfalls, just as the original show did. I like them all, though Star Trek is the oldest friend.
TNG introduced the ensemble cast format, which I have never really been a big fan of for any television show.
DS9 showed the concept could work in a setting other than a starship, but then it failed to hold that premise and introduced its own ship. It's as if it tried to be two shows in one.
I liked Voyager because it had some of the wildest mind-bending stories ever presented.
I'm still digesting Enterprise as I wasn't able to view the entire series until this year. It took a lot of chances, some of them worked and others didn't. It does have some of the most impressive visual effects of all of the series.