I install them both, in your area there won't be much difference other than pricing and how the cables are run, DTV is going to be more expensive ($45 per month + $5 for every receiver past the first one), Dish is cheaper ($45 per month (for the "same" package but they have a cheaper one for $35 per month) + $5 for every 2 receivers past the first 2)
DTV is easier to install (straight runs from the dish to each receiver), Dish is harder (1 Run from dish to receiver then 1 from the receiver to the 2nd room)
DVRs are $6 per month for both, Dish is free, DTV is $100 with $100 rebate, The old DTV DVRs (R10 and earlier are tivo based) are awesome, the new DTV DVR isn't tivo based so at this point it isn't much better than the Dish DVR (But it still is better).
Dish has the edge in HD at the moment (Voom package + Normal HD) But DTV is rolling out the locals in HD. The Dish HD Receiver is free (I think, don't quote me on that), DTV is $200 (Again, I Think, Don't quote me on that one either, We don't do that many HD installs, not much demand in this area).
That should about cover it, Any more questions, LMK,
WTT
P.S. I give DTV the win based on the older DVR units, but if you can't find one, go with Dish due to pricing.