I've recently captured various programs from Dish Network with a R5000hd add-on and from a friend's Comcast Motorola box via the firewire method described
here.
I don't see too much of a difference between the two providers when it comes to the 720p stuff (ex FOXnews, A&E). But the video can vary a lot between channels broadcasting in 1080. I can finally see the pixelation, macroblocking in the Comcast video that a lot of subscribers are complaining about - not too bad in static scenes, very noticeable in fast moving scenes (as bad as my local NBC/CBS OTA stations.)
But then Dish looks like it adds this very thin layer of vaseline with their 1440x1080 HD-lite:
http://screenshotcomparison.com/comparison/148173
http://screenshotcomparison.com/comparison/148170
I'm curious to see how Directv stacks up PQ-wise as I would like to switch to a provider carrying AMC once my free HBO sub expires from Dish.