"Firefly". No question. Fox really badly handled this Joss Whedon sci-fi gem largely because Fox didn't understand its audience. Firefly only ran 13 episodes and Fox bounced it around the schedule so much nobody was really able to find it. Those that did were hooked on it. After Fox managed to mishandle the movie version, they pretty much buried it so it could never be revived.
Too bad. Firefly had the potential to draw a lot of sci-fi viewers that had long ago been turned off by Star Trek's inexplicable pie-in-the-stars smooshy liberalism after James Tiberius Kirk retired.
Firefly was a gritty look at humans once again on the frontier. The space western feel made sense to hard sci-fi fans and the lack of encounters with big-headed rubber aliens cleared out most of the horror movie fans. Firefly was the thinking man's science fiction and had people had time to find it and watch a few episodes, they'd have been hooked and have been if they watched the series on the Syfy Channel or one of the Science Channel marathons or borrowed some Firefly groupie's DVD set..
Firefly fans are more fanatic than Ron Paul supporters. The cast was perfect and every one of them has said they'd do the series again in a heartbeat. Nathan Fillion, Firefly's Captain Malcolm Reynolds, manages to sneak a few Firefly references into his new series, Castle. The rest of the crew do appearances at conventions and to a person call the Firefly series one if not the best acting work they've ever done.
If you have not seen it, jump onto a Sci channel marathon some weekend when they run the whole series and the movie back to back. You will not regret the day wasted unless you're an ignorant boob and then, don't worry. Fox still has plenty of reality TV shows where they eat worms and stuff. You'll be alright.