I'm no expert, but here is what I know:

Combination of Watts and KV's would be a good comparison between motors since it shows the power (watts) and speed (KV's).
The Amps will give you the limitation on the motor and determines the type of ESC to get. I usually get an ESC rated higher than the motor's max amperage to be on the safe side. To avoid motor/battery damage, I use a wattmeter (Watt's UP) to measure amperage at full throttle and make sure I don't exceed the amperage limitations of the motor/battery/ESC combination.
Motors should also come with data regarding limitations as to prop size (min to max). Size and pitch affects power required (amps).

Hope above helps out.