T O M O R R O W ' S S I T C O M C L A S S I C S: WHO WILL RULE IN RERUN? The law of survival of the funniest will weed out mutations like "Home Improvement" and "Roseanne" -- but they'll still be howling at "Friends" in 2020. BY JOYCE MILLMAN | Illustration by Johanna Goodman you've got the milk and cookies, the remote control and the TV Guide. It's been a long day and all you want to do is zone out in front of an old sitcom and laugh. Would you rather watch: A) The Edith-gets-raped episode of "All in the Family"; B) The Alex-grieves-for-his-dead-friend episode of "Family Ties"; or C) The one where Lucy gets her head stuck in the loving cup? Easy, isn't it? (I'm assuming that you picked "C" and we're still friends.) Classic sitcom reruns are the comfort foods of TV. Familiar and aglow with pleasant associations, they're like family photos that you never tire of looking at again and again. The purpose of a sitcom rerun is to take you to a happy place -- and if it doesn't, well, what's the point? Why not just watch "ER"? Based on an entirely unscientific sampling of sitcoms now in rerun on Nick at Nite and other channels, I submit that there's a Darwinian theory of rerun longevity at work -- the survival of the funniest. The sitcoms that bear up best over the years are the ones that stick unashamedly to carefully-honed comedy and don't get heavy-handed or Very Special on us. As "Cheers" or "The Mary Tyler Moore Show" or the best classic sitcom around these days, "The Odd Couple," proves, it's possible to do heartfelt stories about common human experiences -- life 'n' death 'n' stuff -- and make them laugh-out-loud funny and treacle-free. What else makes a classic sitcom a classic? Watch "The Dick Van Dyke Show" and anything starring Bob Newhart to appreciate great comic acting and vivid characters. Political correctness doesn't count for much in Rerunland: The most enduring (and endearing) sitcom of all time, "I Love Lucy," is also the most hopelessly sexist. Topicality can be a liability, too; the "Murphy Brown" reruns airing now in syndication are already painfully dated, with all those lame Leno-esque jokes about Dan Quayle and glasnost. (By contrast, "The Simpsons" reruns, though just as topical, seem as fresh and sassy as the day they first aired -- 'toons can get away with anything.) Campiness can take a sitcom pretty far in rerun -- just look at "The Brady Bunch." And, as fans of "The Addams Family" and "Green Acres" know, a good sight gag is a joy forever.