Both services are pretty much the same. Dish does offer a lower priced opening package, the Top 60 that with locals runs about $32. a month. DirecTV's starting package is $10. higher per month.
First time customers with credit cards and decent credit basically get their equipment for free with both companies.
If you like High Def, or the digital video recorder, DVR, then Dish is cheaper up front for a new customer. You lease the equipment, and return it to Dish when you decide to close your account. DirecTV charges extra for those specialty receivers.
Both companies change their promotions every quarter. I recommend contacting a local dealer and find out the current promo best for you.