Thanks for the info Newt.
I had a 46lbs Minn Kota on the old boat (that's the motor my wife gave away) and I have a 43lbs MotorGuide motor on my current bass boat. I can honestly say that I haven't noticed any difference in how long they run on a battery charge, at least not until I doubled the battery capacity on the bass boat. Logically, the thrust is proportional to current, so there shouldn't be any reason for one motor to draw more current than the other, except for the small difference in thrust of these two motors.
That aside, if I were buying/specifying a new trolling motor I'd probably go with Minn Kota, although there's no logical reason for the choice.