Since you've been here a while, surely you've noticed this is about the most common question. However, I'll throw another shot at it.
1. If you simply must have the NFL Sunday Ticket for $200-$300 (SD/HD/etc) then there are no further questions, go with D*.
2. In various forums people have posted their measurements. The PQ on E*, both SD & especially HD, is better. D* compresses and bit starves their product more, and it shows so much they are often accused of transmitting "HD-Lite." ALL providers could do better- sat & cable could compress less, and OTA could drop the multicast idea when they are transmitting HD. Overall, OTA will give the best HD.
3. Tivo has been generally viewed as better than any other brand. However, the Tivo-D* contract ends in 2007. D* no longer pushes Tivo, although they will provide the box if asked. Future boxes from D* will be branded D*, and most are expected to be built by NDS, another company controlled by Rupert Murdoch (who controls D*). These boxes are expected to have features the Tivos won't. We'll see. There might not be a Tivo MPEG-4 HD DVR. The E* 942 is highly rated. Some prefer it to Tivo- matter of taste and your tolerance for the Tivo reporting features, etc. The upcoming E* 962 is basically an MPEG-4 version of the 942 HD DVR. All of today's satellite receivers will be replaced over the next 3 years or so.
4. E* has more HD today, and will likely continue to have more national HD channels as they add the remaining Voom channels (& others) at the start of the new year. D* seems to be moving more toward HD Locals.
5. E* is usually, but not always, a bit cheaper than D*. Both usually beat cable.
These things will change over the years. But you can always change your provider over the years, too. Unless you must have the ST fix, E* is your best bet today.