Seinfeld all the way for me. A decade plus after its final episode we're still quoting multiple lines from Seinfeld on a regular basis. No other show has really been able to do that. George and Kramer especailly are genius.
Sometimes I'd start to laugh hysterically into myself when some Seinfeld moment pops into my head for whatever reason.
Last time I recalled the scene in which the mohel was bitching on Elaine about putting the glass on the edge of the table. Or the one in which Kramer goes to watch a film with a cafe latte hidden down his trousers and the guy is like "Do you have one of those caffe lattes hidden in your pants?" That was really too funny. A lot of George moments obviously too (he has most of the best lines).
I've watched Seinfeld episodes more times than I can count and for the most part they still keep their integrity. I just didn't get near that level of 'buzz' at all with what I tried of AD.
I'd pick Seinfeld here no contest if forced to watch just one of these shows ever again. It's pretty much the absolute pinnacle of the sitcom as far as I am concerned and have great rewatchability.
Which do you prefer (if any at all)?