I used to have Comcast for my TV and internet. When Verizon ViOS was installed in my area, I checked it out immediately. Verizon offered me better prices for more TV channels, and higher internet speeds. So I switched almost 2 years ago, not a single complaint about Verizon's service.
Given the choice between the two, I'd take Verizon FiOS any day.
Oh, and to address your concerns...TV reception is great. My HD channels look incredible. Shows like Survivor (when they cut to shots of nature) look phenominal.
As for internet speeds, my only complaint is when my computer decides to be a piece of shit and freeze, but that has nothing to do with the FiOS.
Overall, the only gripe I have with Verizon are that their HD DVR boxes are like $16/month, where I remember Comcast's being like $9. But whatever...