I went from comcast to fios and as much as I hate to say it, as soon as i'm eligable for "new customer" discounts again, i'm going back to comcast. Picture quality is somewhat better on Fios and programming is about equal. But I do have two huge beefs with Fios:
The DVR totally sucks. Hard drive is too small, don't really care for the interface, but mostly the IR recievers on the damn box are just weak. You have to be right in front of the damn thing for it to register a command, whether with the supplied remote or the universal I use. This is a fairly common complaint with these motorola boxes.
Secondly, I hate that in order to get more than the local channels and a few others (TBS and a few spanish stations) you have to have a cable box. With comcast just plug it in and you've got 1-99.
The on demand offerings are pretty weak too. On the upside, they do have MTV HD if you want to watch Fall Out Boy or Missy Elliot in concert 20 times a week.
I really wanted to love Fios TV but now I'm just waiting to switch back. Dig the Internet service though. Fast, cheap and rock solid.