I recently got in trouble for saying "They are all cooks" meaning Sat and Cable TV providers.. WHY, because they all try to UP-Sell you, a form of bait and switch, and they all mislead you as well... But that's a long story and told elsewhere. I don't wish to go over it again.
So, Sat-101
DirecTV is suspending or elimination SD transmissions.. going all HD, and rumor has it ending even HD in a few years but I have to question that rumor..
DISH, has no such plans far as I know.. They also have the pay as you go plan.
DirecTV can sell you "Distant Network Service" This is great for RVers because you can pick from either east or west coast NETWORK (ABC, NBC, CBS, and so on) Stations and no matter where you are, NY, LA (the two citeis) Kansas, Ohama, Dallas, Darian (Where I am near) You get network TV.. Dish is injoined on that and can not so you have to call 'em up and give 'em your new zip code when you park. if you move too far.
Now, there are 5 types of antennas. ALL ANTENNAS need a clear view of the satellite arc.. All types.
"Dish Types" either roof mount or ground mount (manual) These antennas are matched to your receiver and they work, Period, one or two receivers or a dual/multi channel DVR they work, Period (Type 1 and 2)
DOME type antennas come in 3 types.. Rooftop Stationary, Rooftop "In-Motion" and portable (That's the other 3 types)
Domes typically can see ONE sat at a time, and no dome currently made can do DirecHDTV.
Dishnetwork uses 3 satellites so a Dome works great with a SINGLE receiver like a VIP 211 series.. But if you have two or more, or a dual/multi channel DVR. you will run into conflicts. Better to use a dish.
Now the Rooftop v/s ground (I recommend one of each)>
If you are parked under the evil signal eating tree, Rooftop no work. Period. But a ground mount with enough RG-6 just might clear the tree.,