+1
I love (and miss) Firefly but I had to vote for BSG. Whoever said that Firefly DOESN'T use witty comeback lines is way off base. That show was all about the witty comeback lines (which I love). And it made me a fan of Fillion's.
But BSG is what has made me take sci-fi more seriously. Yes, I used to watch STNG religiously when it was airing at the time, but that's mostly because it was the only game in town then and we had turned it into a social event, with friends coming over to watch it with us. So that was more about the experience than the actual show.
BSG is one of those shows that fits into its mold perfectly and yet transcends it completely. I hope that makes sense to someone else here, because I think it explains my feelings about the show well.
Amazing realism, grittiness, characters, writing, effects, storyline. It balances the overarching story with the minutiae of individual stories. It doesn't overdo the sci-fi parts to the extreme. That is, people are using scotch tape dispensers and normal-looking tools to fix things, doctors don't point magical handheld devices at patients to cure them with some sort of laser-technology, and ships come in for a landing on the battlestar in a rather haphazard way. It's like all the details of balancing "regular" technology with "sci-fi" technology were thought out clearly and logically ... making the show that much more believable.
It makes me want to write sci-fi. And that's saying something.