I had Comcast for over 10 years. Customer Service was a BAD joke. Their connectivity for both cable and internet progressively deteriorated until I could have done better with an inside TV antenna (impossible for my location) and an old modem. When FiOS was offered in my area, I dropped Comcast like the proverbial hot potato!
Comcast has tried to repackage itself as Xfinity. Their commercials sing the praises of their in-home WiFi but what good is it if the internet speed is way below that of the WiFi? Yes, you could transfer files or play games within my house at a high rate but just how often does that happen? Xfinity's problem is that copper wire dooms their internet speed to a relative creep, and their cable is prone to drop-outs and pixelization. Add to that, the number of people on your "run". Copper wire can only handle a limited number of connections. FiOS' fiber optics can handle over 100 times the distance, over 100 times the bandwidth, and over 1,000 times the voice channels.
Bottom line(s):
1.) If you transfer lots of files or play games, all within the confines of your home AND do not have/want direct wires to your computer devices, Xfinity may be right for you.
2.) If you are only interested in the $$ bottom line, the Xfinity may be right for you (at least for the time being).
3.) If you live some distance from a Xfinity junction and/or there are lots of people in your area on Xfinity, then FiOS is probably a better choice.