I helped a friend faced with similar choice..both are equal devils

but
DirecTV has slightly better customer service than Dish. Moreover if you intend to use Tivo, DirecTivo is best thingy out there (Dish PVR is plagued by issues/poor cust support)
Here in SF Bay Dish has a slight edge in pic quality wrt DirecTV but not by much (Both are MUCH better than Cable). Both Dish & DirecTV compress helluva lot channels which you can see on a big screen TV.
If you are sports crazy-DirecTV is better, If you want International Channels-Dish is better
As a new subscriber, Dish might be cheaper.
Choose your poison! My friend went for DirecTV since he could order sports programming if he liked.
Another Recommendation: Get 'Para Todos' from Blockbuster..you get 52/26 free rentals from BlockBuster

Cheers,
Kishore