3 Major differences.
1: Programming packages. Dish and Direct, epically when it comes to Sports, have different packages.
2: Price: Direc has a policy of rapid price increases,, Dish.. From what I have seen not so much but they too will cha-ching you if they can.
3: Antennas: Now if you use a tripod mounted dish, this does not mattter but
DirecTV offers two levels. DirecTV works with cubes, domes and other "automatic" antennas, roof mounted (provided you are not parked under a tree) in-motion, or not. 1,2,3,4 receivers (or more) with the proper add on switch. no problems (Also works with a tripod dish)
DirecHDTV works ONLY with a tripod mounted or roof mounted Triple LNB Dish, teh domes and cubes can not receive the HD signal.
Dish the proper dome, cube et-al will work with a SINGLE receiver, but for multiple receivers you need a Tripod Mounted Triple LNB Dish.