The title says "favorite" so I guess I have to say reruns of Star Trek.
As a kid though, I liked almost anything scince-fictiony.
Old anime like Mazinger Z, Getter Robo, etc, then later Star Blazers/Yamato.
Character live action like Hulk, Man From Atlantis, Greatest American Hero
Saturday morning like Shazam!/Isis Hour, Space Academy, Jason of Star Command (and the one with that van/tank/ark thing that I forgot the name of)
Nighttime shows like Battlestar Galactica (but not 1980!), Buck Rogers, Quark and Salvage I
My tokusatsu shows like Kikaida, Kamen Rider, GoRangers...
Probably a lot more my old brain aren't coming up with...