i use a 1/2 inch on wheels, axle nuts, and suspension bolts. my 3/8" air gun is capable of +300ftlbs, but that doesnt mean i use it for lug nuts. not only do i not want an air gun rattling in my ear for any longer than it needs to be, and you put more wear on a 3/8" gun doing lug nuts than you wuld on a 1/2" gun that is more suited to do the same lugs.
i have a craftsman pro 1/2 impact, an IR 1/2" titanium, and a IR 3/8" composite gun. i typically use the craftsman gun on lugs, because it is my cheapest gun.
i also have a 12v dewalt 3/8" impact gun for small bolts, dash work, etc. its fairly small and fits in quite a few places when combined with wobble sockets. i used to have a 18v milwaukee 3/8" gun... it had tons of power for damn near anything i needed to do, but much too bulky. i ended up selling it. if i only had the money for one gun and had no air compressor, the milwaukee would be my choice... but otherwise, pneumatics are still more powerful.
Edited by maozebong, 28 October 2013 - 11:22 PM.