Not quite the old Chevy/Ford debate.. Here is what I advised before and now.
FIrst: A bit of info on antennas. Antennas come in two basic flavors, Domes, which can be portable, in-motion, or stationary, and DISH which are stationary only.
DISH antennas, you get the one that matches yor receiver and it works, (If properly aimed) period, they can be ground mount, or roof mount, auto or manual, does not matter, all that matters is they work period.
DOMES, however, are another matter. With a SINGLE Dish network receiver like a VIP-211,, Most modern domes work, well. Some are better than others but most work well. HD, SD, does not matter.... But install a 2nd receiver, or a dual-channel receiver/DVR. and now your joy turn to sorrow as DISH (And Direct Both) Scatter programming over 3 statllites (Birds) and sure as I'm typing you will want to look at two differnet birds, one with each receiver (not a problem for the proper DISH, but big problem wqith the DOME,, Of course you could put in two domes.
With Direct, SDTV works with the domes, but HD, no joy there period. Domes can not do direcHDTV, just DirecTV Again a DISH type antenna, works great.
Next is Network TV (ABC, CBS, NBC, Faux, And so on) what we call "Locals" DirecTV offers "Distant Network Service" so you can choose to get network TV out of NYC or LA or both for that matter ***IF*** you set it up as an RV account (Home accounts generally do not qualify) that way you can watch your favorite NETWORK shows, no matter.
Dish, is injoined from offering that service, but you can call and get your "local" changed often (so you get local locals)... Bit more work but.. Well.
Next is the programming package. Some folks like SPORTS,, me I like NASA.. NASA is on DiSH, and DirecTV is big into SPORTS. So take a look at the packages, This is my original advice before HD happened by the way, and it still stands.
Finally, Prices.. I will not name names here but one company is great at adding on price.. The other company does a decent job of it too but not nearly as good so make sure you get IN WRITING, the final cost including all taxes and fees before you sign on the line.