As I can't say anything for 50's Prime Time Cafe (as we never seem to have time to eat there), this will be a once sided opinion for now.
DH and I absolutely love Sci-Fi. While the food isn't anything special, it is good, and the shakes are great. The atmosphere is also nice, and we always seem to have a great waiter.
My philosophy is this - try it yourself, and then you know if YOU like it. I never take reviews to heart, unless the place gets an utter 0. I may try it and like it, while my neighbor may not care for it.
I say, choose one (or both) and go and enjoy. Atleast you will know for future trips wether you want to return!!