This is a compare of Denver's Comcast HD Vs. DirecTV HD Quality
I've only compared a few things. I have basic cable. For My high Def I have a Zenith SAT520 with DirecTV. From Highlands Ranch I pick up all of the station OTA (Even KMGH). I recently bought a LG 3100A and decided to hook it up to the cable to see what it could pick up via the QAM Comcast. Well, It got HBOHD, ShowtimeHD, ESPNHD, INHD1 and 2 (although it's been off since yesterday), KUSA, KRMA and KDVR.
I compared OTA "The Tonight Show" to the Comcast "The Tonight Show". The OTA broadcast was clearly sharper. Tonight I watched the U of F game and compared the two. I couldn't discern any difference in picture quality between the two. The few QAM unscrambled channel's that I got looked worse than DirecTV SD. INHD seems pretty worthless, definitely no competition for HDnet.
All this was done with the same cables, both LG boxes via a mechanical switch box. Mitsubishi 55857 TV.