Both Stargates most definitly, then Star Trek (all of them minus DS9) and Firefly, then Eureka ad Sanctuary, though the last 4 are all pretty equal... is hard to differentiate because i like them for different things...
For instance, Kyle XY is technically Sci-Fi, but it acts like a Pseudo Soap Opera... but way less corny... and its just a beautiful show generally. seriously, in a world where all media is about how crappy life is, no matter what your status (compare GossipGirl and Neighbors, for instance, you get all the same crap, and the fact they are from opposite sides of the social ladder means nothing), Kyle XY is a generally feel good show, you just cant help but smile when things go right, and they often do. i cant explain it, but its definitly one of my favorites now...