The Beast With A Billion Backs is the only one of the four that didn't quite live up to Futurama's high standard of quality in my opinion. It was still great though in it's own way and completely watchable. The rest of the three were all classic Futurama to me. If I had to chose a favorite I'd probably go with Into The Wild Green Yonder. At the time it came out, I was still under the impression that this would be the final entry into the Futurama catalog. It was (or I guess "would have been") a perfect ending to a brilliant series.