Decades ago it was always going to be Dr Who, Star Trek, Next Gen, Red Dwarf, Space 1999 and Blake 7 (for the giggles). I also enjoyed the BBC's Hitchhiker's Guide to the Galaxy (both radio and TV versions); oh and Lexx, of course.
However, over the last couple of years I have rewatched nearly all of these and not many stand the test of time - they all had peeks and troughs, except Hitchhiker's, which only lasted one season I think.
But these days I am hugely attracted to Farscape, primarily because it's just so "far out" there, in every sense of the word; just as Lexx was way back in the 90s.
Am also trying (and not for the first time), to get into "DS9" and "Babylon 5" - but it's a big ask, and I rarely get past the first season for each.