Most of the people I know who like Trek are pretty sane, despite liking a pretty poor show. TOS was epic, TNG had its moments, DS9 was relatively good but everyone hated it, Voyager was WARP TEN JANEWAYSALAMANDER SEX, Enterprise was... well, apparently it became tolerable just before it was cancelled.
Star Wars fans are worse. That universe is just unrelentingly bad once you get beyond Empire, and maybe Jedi.
I like Stargate, I must admit. Starts off a bit meh, but then the actors start getting into it, and you end up watching just to see them walk into a boring plot and have fun. Then they introduce Ba'al who is the best villain ever, and thankfully keep him around for pretty much the rest of the show. It gets worse, but... well, SG-1's always managed to pull it together for good episodes even in the more uninspired periods. It also has the distinction of being one of the few SF stories to not only do a time travel episode well, but to do multiple time travel episodes well. Even its clipshows can be good.
I guess I like it because it's nowhere near as serious business as the other major SF shows.
And I <3 Doctor Who because I am British and it's in my blood, along with Red Dwarf and fish & chips.