My vote is for Sci-Fi. They have consistently the best service of the two and the BEST atmosphere. Especially if you are going for lunch. You leave the hot, sweaty, blinding Florida mid-day sun and are dining under the stars. It is good lunch food, and as has been mentioned, the bottomless milkshakes are AWESOME!!!!
50's on the otherhand...
1. They serve more dinner fare- meatloaf and mashed potatoes, fried chicken, etc. VERY heavy for a lunch in the summer.
2. and my big sticking point...service. The first time we went there in '01, DH and I LOVED it! the servers were a hoot, it was like you read in the guidebooks. The other times we have been, '05 and '08...eh. In '08 was the worst, because it was just me and the three kids, and we were sitting there and it seemed like all of the other tables were getting the hijinx and interaction, and our server, when she did come by, was just plain rude. Besides taking our order and bringing our bill, she didn't linger. I was purposely sitting with my elbows on the table. Nothing. Never asked us where we were from,never even brought us the dessert viewer. It was like we were an imposition upon her. So I am never going back, until I read more consistent reviews of the hijinx being spread equally.