Agree with the do your research, just don't take a few responses as the only truth.
The usual path is to research the programming that you want, is there a channel that you MUST have, such as NFL Sunday Ticket, then you want D* or TNT-HD or HBO Comedy, then you want E*. When asking about picture quality, since it's very subjective, I'd recommend that you go to a store and see for yourself to get an idea. I'd also make sure that you check hardware reviews for the receivers that you're planning to get. Both services have problems (some more then others) so see what the general buzz is on how well the STB you're looking to get is receiving on the net. Finally, be ready for a lot of changes coming this year and next. D*'s announced some very agressive HD plans and E*'s been gathering up orbital slots and leaving folks guess what they'll be used for, should be interesting.