I found this on the Campbell Hausfeld site. A bit of help in deciding which compressor to buy.
http://www.ereplacementparts.com/article/1025/Air_Compressors_101.html
Someone will probably tell you to buy the biggest compressor you can afford. Do not listen to that logic.
What are you going to be doing with this compressor? How much room do you have? Do you want to be able to move it around? Do you have 220v in your garage? Are you planning on staying at your current location for many years? Do you own or rent your house?