I always feel odd about voting in polls like this because I feel I should be familiar with a majority of the shows listed in order to have my opinion be substantial. The list has 35 unique items (for some reason, Twilight Zone is listed twice) and out of those, there are only six that I’d consider myself to be intimately familiar with, three that I should be familiar with, but watched long enough ago that I don’t remember them well, ten of which I’ve seen fewer than five episodes, leaving the biggest category to be 16 of which I’ve never seen a single episode. Don’t get me wrong; I love sci-fi, I just don’t watch that much television. (Two of the ones I’m more familiar with I’ve actually never seen on broadcast television, but have only seen pre-recorded.)
So, I’m going to give my vote to Twilight Zone, but I still think: I’ve heard people rave about X-Files and Twin Peaks, but I’ve never seen even part of an episode of the former, and the latter I’ve only seen the pilot episode, and wasn’t aware it was considered sci-fi! (Actually, even though I’ve seen most of Lost, I’m not sure I would call it sci-fi either, and TZ is a bit of a mixed bag as well.) I would have given serious consideration to Futurama or Quantum Leap if they’d been options, although QL is also not so much sci-fi as something like Touched by an Angel with less schlock and time travel used mainly as a plot device.
Oh, and 404? I regret to inform you that Doctor Who, which was a very close second for me, is now in third place, having slipped behind The Sarah Connor Chronicles.