I want to start by saying I have no dog in this fight. Completely unbias. Just bored and wanted to share my expierence.
Growing up my family had Comcast, when I went to college I decided to get Comcast (at about 6 different locations over 4 years). Over the last decade I've spent dozens of hours dealing with service issues, billing, installation etc. You name it and I've had an issue with it and had to call Comcast. Friends and family would call me when they had an issue involving Comast becuase I was so expierenced dealing with the countless headaches 
that comes with dealing with cable companies.
Last September, I moved to a new apartment complex which only allowed Xfinity or Verizon cable and internet. No Dish, no DirecTV. I was sick of the numberous problems I had with Comcast over the years, so I decided to go with Verizon and see what this fios I had heard so much about was all about. It's been a few months now with Verizon so I thought I would share my expierence. I still have and use my comcast username that I've had forever because my parents still are with Comcast.
Comcast is better than Verizon.
(reffering only to residential TV and internet, I'm not talking about Verizon Wireless and I couldn't tell you which offers better home phone service, do those still exist? 
)
Everything I disliked about Xfinity is just as bad if not worse with Verizon. The "free" installation cost about $65, until I called and had it corrected. Verizon is a tiny bit more expensive in general I've found. My internet is slow and I get kicked off all the time, when changing chanels the layout of the menu is strange and unintuitive, Xfinity also has a much more user friendly on demand with more programing, Verizon did not give me free HBO for 3-6 months or anything like that (which Comcast has always done, if you ask nicely 
), the Verizon customer service is bad, the guy who came to instal the cable was not friendly (not a huge deal, just saying), and most importantly the sports package Verizon offers is terrible. Although Comcast doesn't offer Fox Sports 2 at all and doesn't show beIN Sports in HD, the Comcast sports package trumps the Verizon sports package. The channel packages in general do not match up to Comcast. I prefer the Xfinity app for watching TV on your phone over Verizon's as well. Much faster and doesn't lag. I've actually watched live TV on both apps side to side on two cell phones (both brand new samsung galaxy) while connected to the same wi-fi. Xfinity TV Go > FiOS Mobile.
I'll go with Comcast next time. But, this is just one guy's expierence. Take from it what you like. A lot of it probably comes down to personal preference because a large majority of the features, prices, quality etc. are identical.
Oh and the Xfinity wi-fi hot spots that are everywhere are another HUGE plus that Verizon doesn't offer, which ironically saves me a lot of data on my Verizon cell phone.