Okay, okay. I chose Mork, but because of what Robin Williams was able to do. I mean, he managed to take an abortive attempt at shark jumping (yes, I'm fully aware of where the term comes from) and spin it off into a not so bad show. Oh, and then go on to become one of the funniest people in show biz.
Alf was good---nay, great---but he just didn't seem to get the longevity. He did come back in pog form for a while, but Milhouse van Houten was the only one who seemed to care.