Seinfeld is one of the few that everybody concedes was excellent and there's not much of a debate to be had. Look at now and how abysmal the frontrunners are. We have shows that the entirety of the show is beating the same joke to death relentlessly (GET IT THEY'RE NERDS THEY SAY SOCIALLY AWKWARD NERD THINGS ISN'T THIS FUNNY HUH HUH HUH) whereas Seinfeld had an endearing, ridiculous creativity to it that is sorely missed.
Seinfeld was just plain funny no matter what the subject at hand. That sitcom was said to be "about nothing" and it was. Each episode had several both interlocking and unrelated themes, but they somehow meshed into a coherent whole that was funny throughout. Historically, I guess it is the equivalent in popularity to I Love Lucy, but for my generation the humor of Seinfeld well surpassed any other sitcom.
Seinfeld is one of the most perfect shining examples of how a sitcom should work. Lovable characters, memorable quotes, and a simplicity to it that is absolutely timeless. However, as long as Arrested Development is my top choice. The writing, inside jokes, community that follows it so passionately makes it a top choice over Seinfeld. Seinfeld would be a close second.
Seinfeld was a huge show when it aired and loved by millions. Many people still watch re-runs of the show religiously too. It is a great show but it not the best of all time. Fresh Prince of Bel-Air, Martin, Curb Your Enthusiasm, The Sopranos, and a few other shows are better in my opinion.