Provo, UT, is interesting. It has both Google Fiber and Comcast. Their performance is essentially the same, with perhaps a very slight edge to Comcast. I tried to compare them in the other Google Fiber cities, but Provo was the only one I saw both Google and Comcast in. (Austin, TX, is interesting, because that is supposedly a Google Fiber city, but Google Fiber does not show up in the report).

Comcast has similar performance in all the cities I've lived in as an adult (Los Angeles area, Silicon Valley, Seattle, small towns on the west side of Puget Sound). Certainly not what I expected given all the complaining I see on the net about Comcast and YouTube performance.