i personally use a 1/2" one that goes from 10-150 ft-lbs. The larger wrench makes it easy for me to apply light pressure until it clicks rather than use a smaller 3/8" (well they usually are shorter in length) and apply more force to get it to click.

btw, what kind of torque wrench do you guys use for the axle nut? Mine doesnt go high enough for it, and im wondering where to get one... or does autozone rent one that torques enough for the axle nut?

oooooh and my torque wrench is exactly like that too. I got it from tirerack i think for $20. For something that cheap, i dont think it matters too much what size you get. I plan to get a 3/8 drive that covers 5-20 ft-lb (marked in inches) for small ass stuff, and use this one for general stuff.