First, Echostar, which is the parent of Dish Network, has recently bought DirecTV. As with any merger, it's probably at least a year or two away from having any impact on what the consumer sees. The deal won't even close until the second half of next year (assuming FTc approval, etc)
Dish has more HD right now. HBO, Showtime, and a CBS HD feed, which may or may not be available in your area. DirecTV has HBOHD and a new channel HDNet (
www.hd.net).
For HDTV with Dish, you'll need two separate 18 inch dishes. Your limited to only one choice for your receiver, the Dish 6000.
For HD with DirecTV, you can choose from about half a dozen receivers from different manufacturers, and you'll need one oval dish, with multiple LNB's.
If you have any interest in sports packages like NFL, Major League Baseball, NBS, or NHL, DirectTV is the way to go, since they are the one with these packages availalble (not in HD though)
Picture quality is about the same with each.