I would have to say:
Outer Limits 1963
Outer Limits 1996
Variety is the spice of life. Each Outer Limits episode had a different cast, set, and writer unlike many of the other series which had the same cast, set and writer week after week. Twilight Zone had some excellent sci-fi episodes, but it was also heavy on fantasy and horror, so I don't consider it pure sci-fi.