I would wait until mid to late July to make your final decision--the MTN will not air on DirceTV until Aug 1. Dish Network offers a nice high-speed internet alongside their TV, so if they follow DirecTV and add the MTN, you could drop the cable all together.
Dish has a much nicer DVR as well, but they offer less HD programming for twice the price of DirecTV, so it really would come down to weighing what you really want out of you Dish provider.
Then again, if the DirecTV proves to be an exclusive agreement or Dish doesn't add the MTN, you decision in July becomes easy.