My analog channels from Comcast are better than the 100% Digital quality local channels I receive from DirecTV by far. I can't watch the Salt Lake locals from DirecTV on my big screen TV's... I can only stand it on the 14" TV I have in my office (mostly because I don't look at it!). The Comcast analog channels are different but about the same PQ as the best digital from SD from DirecTV.
When it comes to HD my old fashioned antenna on the roof and Comcast are tied for the best HD available. Dish Network (when I had it) was second and DirecTV is by far the worst HD I can get. I'm not sure what DirecTV does to their HD (other than lower the resolution and bandwidth on some) but there is no question that Comast in Salt Lake beats the pants off of DirecTV for HD. For me Comcast has more channels and they are REAL HD not the wanta-be HD Lite stuff from DirecTV.
I spent an an afternoon at a friends house comparing the Sci-Fi channel between C-Band, Digital Comcast, DirecTV and Dish Network. We ranked them in the following order:
1st - C-Band.
2nd - Dish Network
3rd - DirecTV
4th - Comcast Digital
The analog C-Band was way out in front. Better color, higher resolution, better contrast, no digital artifacts.
Dish Network and DirecTV were close but we gave a slight edge to Dish Network as it had a little less artifacting but both were pretty washed out and nasty looking compared to C-Band.
Sadly - Comcast Digital had the least amount of detail. A little less digital garble but the softest picture of the 4. I say sadly because when it comes to HD Comast, OTA and C-band are all tied for first!
Just because something is digital doesn't make the picture better. I'd say its possible to get a better digital picture than an analog picture but non of the providers consider SD PQ important enough to do it well. They care more about quantity the quality so the picture quality suffers.