Depending on what's most important to you, you should consider:
Power source - Masterflow has two options for powering our portable air compressors. Plug into a vehicle's power outlet (aka cigarette lighter) or connect directly to a vehicle battery. Be sure that your power outlet is rated for 15A/180W or you'll blow a fuse and instead should chose a compressor that powers from the vehicle's battery.
Use - All Masterflow air compressors are going to inflate tires, if you just want to top off your tires, you can use a smaller air compressor, if you're an off-roader and want to air up quickly, a larger compressor is going to do the job faster.
Tire size - Passenger vehicles/bike tires/motorcycle tires/mini pick up trucks will air up just fine with a smaller air compressor powered by the cigarette lighter (MF1035, MF1040 M1A1). Midsize tires on SUVs/RVs can use MF1050, MF1089, M240. For larger tires like tractor tires (35s and up) MF1089 will have you up and going in no time.
Inflation time - All Masterflow air compressors have super fast inflation times. However, if time is important to you, just remember, the bigger the motor, the faster the inflation time.