Seen every episode, most in the first run since I was in college when it started... It hit just right on a Thursday night to watch it while drinking then go out with fresh material to the Landing and Doug's. So I am one of the biggest Seinfeld fans you will find.
However, I now have it ranked #2 behind The Office in my all-time greatest list. I can't even explain it - I never thought Seinfeld would be replaced - but that's where I am now. I think of The Office as timeless, where you can go back and watch any episode at any point and you're in. Seinfeld had some episodes that were totally of that era and wouldn't mean much to people today. Seinfeld probably had higher highs, but also a few duds.
*Trivia - Greg Daniels (creator of The Office and Parks & Rec) worked on Seinfeld for a short time. Not to mention being a writer for SNL, The Simpsons, and then he created King of the Hill. That guy probably deserves more credit (or blame) for my sense of humor than almost anyone alive.