I don't think that there are major differences in the picture quality of the HD boxes, but you cannot compare DirecTV's HD against Dish's HD because the differences is likely the compression from the sat company instead of the hardware. You would only be able to compare each via OTA stations. From what I gather, there are a couple of units that have had some bugs, but I don't know which off the top of my head still have them and which have been fixed.
AVS is definitely the place to check out for this answer. They think people are crazy to spend $250 for an audio interconnect, but have no problem spending $250 for a video cable...
Mostly, I would look at what features you need, such as VGA/RGBHV, Component, DVI, Firewire, if it has an RF remote (if you need one) or some other feature. Once you get through that, you may not have much of a choice left...
AVS is definitely the place to check out for this answer. They think people are crazy to spend $250 for an audio interconnect, but have no problem spending $250 for a video cable...
Mostly, I would look at what features you need, such as VGA/RGBHV, Component, DVI, Firewire, if it has an RF remote (if you need one) or some other feature. Once you get through that, you may not have much of a choice left...