I think Friends is better than Seinfeld. Seinfeld was certainly quirkier. But Friends was a game changer. I think Friends feels less groundbreaking now because so many sitcoms since have been modeled after it. Seinfeld had a formula that it's almost impossible to copy. In that sense, Seinfeld is one of the best and most original shows I've ever seen.
The downside is that I don't think that brand of humor holds up as well over time. When it worked the humor was untouchable. But it missed as much as it hit. And when that brand of humor misses... yikes. Friends might have been safer (less risky in terms of style of humor), but it was also more consistent for longer.
Having said that, I still think both shows went on a couple seasons too long.