Sorry to resurrect a dead thread, but I wanted to post a follow-up here, hopefully it can help others who are trying to make a decision between Shaw Direct and Bell. After watching a lot more of Bell lately, I made the switch.
The Bell picture might not be quite as sharp on still or slow-moving scenes, which is in line with what others have said, but it's close. And there is occasionally some noticeable macroblocking in scenes of fast motion depending on the channel. However, there is much less of it than on Shaw Direct (where it was a constant distraction). On most Bell HD channels, it doesn't seem to happen at all.
My suspicion is that Bell is better at dynamically allocating bandwidth to where it's needed, or to more "important" programming. Even though both services pack about the same number of channels onto each transponder, the big sporting events, for example, tend to look better on Bell.
Overall, I'm happy with the switch. In my opinion, a (possibly, and only very slightly) lower quality picture, but one that's consistent, is preferable to the huge drop in picture quality during motion or scene transitions that are common with Shaw Direct.
As for other factors, SD does seem to have better customer service, while Bell receivers are superior (with the possible exception of Shaw's 630, which I haven't used).