I can tell you that my dish is sitting on the floor of my deck and I get high 80s signal strength.

If you plan on getting Tivo, DirecTV wins hands down due to the dual tuners. If your TV is 32" or less (non XBR) I would also recommend DirecTV.

Cable wins if most of the programming you watch is on the analog signal and you have a high-def TV. Lots of digital artifacts appear on DirecTV when you have a good TV.