I have on board air on all 3 rigs. On the Mule and the Gecko I used the ARB HD compressor rated for tire inflation as well as locker operation. I also used a ViAir 2.5 storage tank with each of them. These compressors have a 50% duty cycle which means they can run non-stop for 30 minutes and then they must cool off for 30 minutes. They are sealed so they can be installed in the engine compartment and they come with pressure sensing shut off switches, etc so they fill the tank to 90 psi then shut off. You can also plumb the air intake to the inside of the vehicle to ensure clean air going in to the compressor. The Mule has 37's and the Gecko has 39's which I usually run down around 2 psi with the beadlocks. The ARB compressor with the air tank will fill all 4 to 20 psi in less than 30 minutes, so I have never had the duty cycle become an issue.
On the Meanie it came with a ViAir 450C and 1 gal tank. The 450C is rated for 100% duty cycle and will go up to 150 psi.
I don't think you can go wrong with a ViAir unit. I get my stuff like that from 4 Wheel parts, they seem to have good prices. If you only use it very occassionally and for light use one of the HF units might be OK.
If you want faster fill ups get a compressor and air tank rated for 200 psi, then put an adjustable regulator on the output. If you are operating air lockers you can't go over 90 psi or it can blow out the locker seals.
Which every way you go I agree with UB and suggest you get a storage tank. Even on the Meanie with a 1 gal tank, you can operate the air lockers all day long and never have the compressor kick on.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang