I am admittedly an E* sub (7+years) and I have no experience with D*, so my response may be somewhat biased tho' I'll try to be objective. As a new sub for either service you should check with both (perhaps several calls to each) to see what packages/incentives/commitment periods either is willing to offer. That may be more important to you. You might also want to call a local installer for their suggestions, preferrably one that sells/installs both.
From what I've read in these forums:
1) D* will be your choice if you're oriented to the sports packages.
2) D* currently has more satellite capacity and I believe is ahead in terms of LiL coverage. E* is catching up.
3) E* recently released their first gen MPEG-4 equipment. I haven't seen a definite date for equivalent D* equipment yet. That may not make any difference to you in the short term, but almost all of E*'s LiL HDs will be in MPEG-4 and both services will migrate in that direction as more HD content becomes available.
4) E* is currently offering 25+ HD channels with their "metallic" packages and premium programming (23 I believe without the 2 premiums). You'll need the MPEG-4 capability to get 7 of those (even tho' the programs themselves are not actually in MPEG-4 yet). Not sure what the D* count is at this time.
5) Almost all sat HD programming is "HD-lite", i.e., compromised PQ, but E*'s PQ is reportedly superior "by the numbers" in terms of resolution and bitrate. I will attest to the "almost HD" look I've getting with the voom channels as compared with the single OTA channel I currently receive (which is at 1080i). HDNet and ESPNHD are suburb on E* and probably on D* as well. More to come, I'm sure...
6) Both E* and D* have migrated to lease programs, tho' E* will still activate sub-owned equipmemt. You'll have to compare the quoted rates to see what makes sense to you there. As a new sub I'm not sure that you'd be entitled to any of the remaining "legacy" offers from E* however - YMMV.
Hope this helps!
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