If you're interested in HDTV, Dish Network is generally better choice than DirecTv:
1. Dish has significantly more HD channels. The Voom HD package currently provides 10 additional channels that DirecTv lacks. And in earily January, the Voom package will expand to a total of 15 channels.
2. Dish has far superior HD picture quality. Most of their channels are presented in true 1920x1080i resolution and look tack sharp. Every single one of DirecTv's HD channels has been down-resed to 1280x1080i, resulting in a softer picture.
3. The one area where DirecTv has the lead in HD is for local network channels (i.e. ABC, CBS, NBC, Fox). They have been more agressive at going after this than Dish. Although if you are not in one of the top markets (i.e. LA, NY, Chicago, San Fran, etc.) then this is of little benefit. Personally, I find local network TV to be generally poor and perfer the shows on channels like HBO, Discovery & PBS, so I find Dish's strategy of focusing on national HD cable networks to be more to my liking.
The other thing worth pointing out is that the DirecTv Tivo units are nearly obsolete. Because the new DirecTv HD locals use MPEG4 encoding, none of the Tivo units will be able to receive those channels. Your only option is to buy DirecTv's new in-house produced DVR which is not nearly as nice. It's really sad to see them do this because I have always been a big Tivo fan and owned one for years.