Greetings.
"Seinfeld" for me. My choice depends on a number of mainstream reasons. The most significant being that "Seinfeld" chronicles are actually funny in a more complicated way, rather than the all too obvious and blatant humor of "Friends." I suppose it is taste, and in this particular circumstance I am not afraid to call "Friends" moronic next to "Seinfeld."
However, upon analyzing some characters from both shows, "Friends" does a better job in exploring each character's journey, with great portrayal of the effect of life on an individual. "Seinfeld" doesn't necessarily explore each character changing deeply, and despite the twists and turns of life, the main characters remain as they are, with George endlessly selfish, etc. This is just my take on it and I am sure it is only a tip of the iceberg, with more analysis available. Again, it is preference, but in my opinion, humor is really funny only if it is concealed first, and not shot straight to the face with a simple thing such as having characters endlessly go through small "funny" situations that only produce horrid background laughter, something that only annoys me more when I watch "Friends."
Well, this is my take on this.