Most likely Firefly is one of my favorites. Farscape is very close behind it. For a few seasons I refused to get into Stargate when my husband got into it because Farscape had been cancelled and somewhat replaced by Stargate.
I tend to prefer Sci-Fi shows, or more mainstream shows with hints of magical realism, to other shows. The Office is a rare exception.
I'm new to Dr. Who with this current series, I adore it but they are loosing me with the constant expendable woman sidekick. I am told by shocked die hard Dr. Who fans that this has always been the case. Just because it's always done doesn't make it right...
I think Battlestar Gallactica is some of the best TV I've ever seen. I think most of the individual best hours of TV I've ever spent have almost all been with Sci-fi shows, though. I appreciate that the people we think we should root for as the good guys aren't as good as we would like.
I tend to read more fantasy than sci-fi.
Love the topic!