FiOS is the better service. Both technically and business-wise, IMO.
It will depend on your area, but I find Comcast to be pretty shady... their advertised speeds are almost never hit. Peak usage times and 'neighborhood-sharing' of bandwidth is still a problem.
I have cancelled their service twice in my life, at two different locations and malicious billing occurred. Once for $400 and the other for $700. Cancelling over the phone is an exercise in futility as they hang up on you after 5 minutes of trying to keep you on their service and offer you this and that.
"Ma'am, I'm moving.. I don't need the service. CANCEL MY SERVICE! CANCEL MY SERVICE! I WANT TO SPEAK TO A SUPERVISOR!"
"Click". They hang up. I had to physically go to a Comcast building to get it cancelled. The "bad bills" came a few months later and had to be taken care of at the courthouse after 8 months of fighting, credit reporting, etc. This isn't a unique story.
Verizon may be only slightly better on the billing side, but at least they haven't acted fraudulently yet.
As an electrician, I worked at many of my regional "hub-sites" for Comcast and it is absolutely shocking how poorly implemented it is. I installed over 15 of these 50kVA generators across the VA area:
Just outside of Charlottesville in a small town of Waynesboro, on the side of a mountain they have a 50'x50' area with barbed wire fencing a few satellites and a $300 cheap metal Home-Depot shed. Inside the leaking, rodent infested 20 year old shed, shed they have a million dollars of rack equipment that serves the Upper North-West area with comcast tv and internet.
The state of the hub sites was deplorable. 90% of them are in what I would call "temporary locations" that became permanent. The other 10% are actual buildings that are leased/purchased or the Customer service centers/downtown office building type deals.
Go fiber. Say no to cable if you can.