Sci-fi is kind of a broad cover, but lets see...
The pinnacle of science fiction television as science fiction was understood in the literary world - that is, science fiction as a way to explore abstract ideas and hypotheticals - was Star Trek: The Next Generation. The first and most of the second (and even some of the third) season were, to put it mildly, kinda shitty, but it had developed into something extraordinary by its closure.
For overall best sci-fi
drama though, it's actually a bit of a four-way tie between the new Battlestar Galactica, Firefly, Cowboy BeBop, and Neon Genesis Evangelion. The latter is very soft on the scale, and both the latter two are animated, so if we discount them on that count, we come up with BSG and Firefly.
In a competition for my favorite - the one I'd most prefer to sit down and watch - between BSG, Firefly, and TNG... I don't know, it'd vary based on my mood. They're just so different. I guess any given episode of Firefly stands a better chance of being good than any given episode of BSG or TNG, so I guess I'd have to pick it as a winner on that count.
So Firefly it is, then.
captainfluoxetine said:
Yeah, I'm kind of surprised DS9 doesn't get more love. It was just
barely edged out in my case, but it's still one of my favorites too. Such well realized characters...