The air master is a plane or helicopter-oriented controller. It has only weak drag brakes and no reverse. The monster pro is a car-oriented controller and has strong proportional brakes, as well as reverse. Quarks are smooth controllers, great for running neu and mega motors, but they heat & thermal often and sometimes burn. A buggy or truggy would be a suitable vehicle for a quark, just make sure you have adequate cooling to it. Mike (owner) makes a heatsink for the qquark 125 controllers, seen here:
http://www.rc-monster.com/proddetail.php?prod=RCM008 I hope this helps. Also, for A123, consider a 2p configuration. The 5s1p would have a hard(er) time getting enough amps to your motor, and could decrease potential performance.