I think we've safely established that the "Rocky" series is the best movie series ever... although the first three "Star Wars" (I mean the first three MADE, not episodes I-III) may be in the conversation. Even so, I have to be in a certain mood to watch Star Wars, or the Godfather (arguably the finest individual film ever made), or even LOTR.
But TV... ah, there's a tough one. And it's made tougher by the fact that entire series--supposedly even very good ones--have come and gone without me ever seeing an episode. But even though I love Seinfeld, and Cheers, there really is no contest. The best ever TV series is certainly MASH. Like "Rocky," it doesn't matter what mood I'm in... if MASH is on, I can watch it and enjoy it. Best character development of any sitcom ever. And if you don't tear up every time Henry Blake's chopper goes down in reruns, you have no heart. Period.