Efficiently turning electric to kinetic energy
I don't think anything beats an electromagnetic motor.  Here's a link to the first result when I googled &quot;Highest efficiency motor&quot;.  It's 99% efficient.  Note that you almost always need a set of gears to convert rotational force into the force you actually need, and a quick search seems to indicate a maximum efficiency of 98% per gear junction.  Note that for some specific types of motion, different methods will be most efficient.  For a high frequency vibration a piezo or quartz crystal might be more efficient.  For bulk power transfer though, motor wins.
Just a side note, volts to footpound is an apples to aardvarks comparison.  You need to compare input power to output power to analyze efficiency.  You can produce the same power level motor in a variety of voltages.