The things to consider are…
Max PSI – “impulse” tools like nail guns need a certain minimum pressure to work properly (listed in the tools specs)
CFM (cubic feet per minute) – “constant” tools like sanders and sprayers need a certain amount of pressure delivered continuously to the tool to function properly. usually it will say “X.X CFM @ Y psi”
Volume (generally gallons) – the higher the volume, obviously the longer you can work between the motor kicking in to refill it. For impulse tools this is less important than for constant tools, which go through a volume of air much faster. Running out of air in the middle of nailing, you can just wait for a bit, running out in the middle of spraying a finish can mess up your project. You can purchase 5 gal expansion tanks fairly cheaply so this is the least important IMHO.
Check the specs on the tools you plan to buy, then compare it to the specs of the compressors.
-- - Jei, Rockford IL - When in doubt, spray it with WD-40 and wrap it with duct tape. The details will attend to themselves.
