Hmmm... I'll offer a different opinion than seemingly everyone else. At my old house (I moved in June), I had Comcast digital cable and did not like the service--lots of drop outs and service problems. When I moved, my intent was to switch to DirecTV, but I still needed CATV for broadband, so I got that hooked up first. The digital was *significantly* better at my new house--signal stronger, less reliability problems. Because I wanted HDTV, I still ended up laying out roughly $600 for an HDTV SAT STB, and subscribed to DirecTV. (As an aside, I thought I'd done the right thing by getting multiple RG6--2--runs to each room, but I still don't have enough inside wiring to support TiVo DirecTV.) I don't think the DirecTV picture is as good as Comcast's digital cable, but whoa! the HDTV looked *good*! I did lose a bunch of movie channels, however. Just when I thought I was happy, I find out that Comcast in my area is rolling out (has rolled out) HDTV over CATV--including the local OTA affiliates. I find both services cost-competitive. Having had both, if I was starting over right now, I'd definitely go back to Comcast for digital w/HDTV and lose the ugly 3 LNB dish on my terrace.
Moral of the story, might want to talk to your CATV provider about their upgrade plans. Also might want to check signal strength in your area before subscribing.