We have both FIOS and DirecTV in an attempt to compare them and decide whether to dump DirecTV. DirecTV has much better HD DVRs, with better remotes (can be coded-not so on FIOS), greater hard disk capacity (and can be hacked for more) and better (more) sports.
FIOS is much better at
everything else: price, picture, sound, does not quit in thunderstorms (a problem in North Texas), needs fewer wires (we have older HR 21s and a 5 LNB dish), networking media, etc. And, even though the FIOS DVRs suck, they are much faster on channel changes and mode switching. FIOS never compresses their HD signal, either. When FIOS says you are getting HD, you get HD, 1920 by 1080, not HD Lite by DirecTV.
All things considered, the advice you already have is good: for sports, particularly for national pro subscriptions and exotic locals, and if the DVR comparison is a big deal for you, go DirecTV. Otherwise, FIOS is a clear winner.
The other things we like about FIOS are that they have no fee for insuring boxes which do not work, and they do not have deceptive "service commitments" for hooking up new boxes. FIOS does have commitments for locking in packages, but if you get a new box it does not extend you, and you do not have to pay for replacements. Oh, and that stupid "HD plus" that D* makes you pay for, with HD NET movies and MGM, etc.? No fee from FIOS, and no special fee for HD.
Although I like the D* DVRs better, I find I seldom use the longer buffers and increased disk capacity anyway. For most people, FIOS is better. Oh, and FIOS HAS VERSUS.
Lastly, we have a FIOS "Triple Play" package, which gives us an enormous price advantage for combining phone, internet and TV. They told me I'd get 20/15 internet speeds. In fact we are getting 25/20. The terrific FIOS internet is something we already had, and could have with DirecTV, but with the FIOS combination packages, the internet is virtually "free," a good plus. We have four DVRS and also streaming Netflix and Slingboxes-we've never had a bandwidth problem.