I voted for The Office, and it wasn't too close for me even though I love Seinfeld as well. Although The Office did decline in its final seasons, I think it probably had a bigger effect on other shows than Seinfeld did, by really bringing the non-studio audience, non-laugh track show into the mainstream. Others had done it with moderate success, but The Office elevated it to kind of being the norm. The mockumentary style and awkward humor were also a bit novel.
That's not to say that Seinfeld wasn't novel and didn't have impact. At the same time, I think maintaining quality in later seasons is its biggest pro over The Office, but I think it's probably easier to write a show that does that when there's minimal long-term character development and the main plot of the show is the characters being generally bad people who find themselves in odd situations. I think the longevity of Curb and Always Sunny kind of affirm that idea.
I'm surprised about M*A*S*H vs Cheers. I guess it makes sense that M*A*S*H might do poorly in this style of tournament due to its age and since it had more drama than comedy in the later years. But I think that adds value because it's a hard thing for a show to evolve in that way and find a balance. I also think that M*A*S*H holds up better than Cheers watching it today, but that might just be nostalgia since I watched M*A*S*H more growing up.
