I've got both E* and D*. I have fairly basic packages on both, plus all of the HD services both offer.
Watching them side by side, I think E* has better picture quality. The DishNetwork 942 DVR is the best satllite receiver I have ever owned, hands-down. E* also has the Voom HD channels, which are a big plus for me. D* has ESPN2 on 9/8, but I doubt E* will be far behind. The one thing D* has that's a big deal for a lot of people is NFL Sunday Ticket.
The truth is that I think they're both really good services. I really don't have complaints with either, and I'd be happy having either of them if I couldn't afford both.
I'd be real cautious, though, about investing a whole lot in MPEG2 equipment of any kind when we all suspect that MPEG4 is just around the corner. Forking out hundreds to upgrade new MPEG2 equipment will not be a pleasant experience. Also, though we hear alot of rumors about future HD offerings on E* and D*, no one seems to really be able to provide the straight scoop on what they are going to look like a year from now.