Right vs Left Crank Power Transfer Efficiency
There will be windup (flex in the crank under force).  Both the drive side (spiders and chain ring) and the non-drive side (shaft, spiders and chain ring) will experience windup during power transfer.  The amount of wind up is however very small (and depends on the magnitude of the force applied), but will be slightly higher for the non-drive side as more components are involved.

That said, once the small amount of windup has occurred (at the start of the power stroke), both sides will transfer force with equal efficiency for the rest of the pedal stroke.  Because the windup is so small, overall efficiency between sides will be essential  identical.  

As an aside frame flex will be a much bigger component, convince your self by locking your brakes and apply force to either crank and see what flexes. I find I have better power transfer with the right amount of frame flex as it allows me to get into a rhythm  that I can best describe as like riding a wave.  Some term this planing.  What ever you call it, a bike and components that are too stiff will feel "dead" for lack of better words.