If you search there are a lot of complaints about the HD picture quality. The problem is with the low bitrate they are using to re-compress the HD, around 5~7Mbps MPEG4 compared to Comcast's 12~19Mbps MPEG2. MPEG4 is about 1.5 to 2 times more efficient than MPEG2, but an average of 6Mbps is still pretty low and leads to macroblocking and blurring during fast-moving and complex shots. However, it depends on your expectations of what HD should look like, so it's a hotly debated subject on these forums.

If HD is really important to you, consider OTA for the locals or DirecTV. Comcast also over-compresses some their channels, so theoretically it should look about the same as U-verse. It may have to do with MPEG2 encoders being more efficient as it's an older and extensively tested standard.