Coke or Pepsi?
Paper or Plastic?
Ford or GM?
Honda or Harley?
What do all these have in common? They are all up to the individual. FIRST thing you do, before you look at anything else...look at the programming packages available on each service. Find out what YOU like. For example, if you want to pay for out of market NFL football games (NFL Sunday Ticket), you want DirecTV. You can stop looking at Dish. They can't offer that package until at the very least 2006 and probably not even then.
However, if you want international programming or certain specific channels that Dish has and DirecTV doesn't, then you want Dish and you can stop looking at DirecTV. And yes, those are your only two choices for US service. That is unless you count Sky Angel, an independent 32 channel Christian service which is available on Dish Network equipment (different company though)
Only if the programming choices and price-points are a wash do you start to look at anything else.
Picture quality is a constant argument. Again, it's in the eye of the beholder. However the consensus is,
Dish = Softer picture with less visible digital artifacts.
DirecTV = sharper picture with noticabley more visible artifacts.
But even this varies from channel to channel. A very detiled evaluation was done on another board and they found that at times the description above did not apply. But in general, DirecTV did have the sharper picture. I take this with a grain of salt because I consider that other board to lean heavily towards DirecTV. But I am not disputing the findings.
IMHO, next comes the equipment and features you want and the price-points you want. This can get VERY complicated because of all the different new-customer deals out there. Who has the best equipment? Most people will say DirecTV. I have had Dish for 7 years and love my service (don't ask about the old discontinued 7100 and 7200 series units though
Great features and ahead of its time, but software nightmares!)
When looking for a new receiver, I cannot empasize enough how much you want to get a PVR (Personal video recorder). PVR is to VCR what an automobile is to a horse and buggy. This is no exageration. There is nothing wrong with recording to a VCR and you can do it with all the satellite receivers, but once you have a PVR for a month, you'll never watch TV the same way again. DirecTV has the DirecTiVos that many here swear by. Dish Network has the "Dishplayer" line.
Are you into HDTV? If so, then the Dish 811 is a great cheap way in (No PVR). If money is no object, then the PVR921 is an amazing machine that essentially does everything but sexual favors! --though some here are having some software issues and feel that they are on the receiving end of some one else's pleasure!
I am unfamiliar with the DirecTV models.
Good luck
See ya
Tony