A windmilling propeller will always absorb more energy and cause more drag than a stopped propeller, feathered or otherwise. If the slipstream is performing work on the propeller and making it turn, overcoming the engine's internal resistance and it's flow being altered by the propeller disc, then you've got a higher drag operation than the same propeller sitting still.
The "depends" part comes into play when you consider the benifits of stopping vs. allowing it to windmill as you perform your drift-down. It depends on how much energy and altitude you'll lose trying to get the prop stopped. If you consider that you're starting from your best-glide condition, then altering it to a higher or lower airspeed in will increase descent and increase drag. You may be able to quickly stop the prop, or it may take some time. How much altitude is lost, how much descent takes place beneath your best glide flight path, will determine if you've lost or gained anything.
Generally speaking, you don't want to deviate from your glide to try to stop that prop if you don't have a means of feathering it, or if it doesn't stop on it's own.
I've experienced engine failures involving props that didn't feather, and wouldn't feather, several times. I've never attempted to slow the airplane down to get the engine to stop turning. Most of the failures have occured at low altitude and I didn't have the option of playing with it. In most cases other engines have enabled the airplane to return to land; in one noteable case I ended up on the ground not far from where the engine quit. In that particular case there was little time from the loss of the engine until contact with the surface, and there was little to be done from such a low altitude.
Most of those cases took place in very mountainous terrain. In most cases I wouldn't have attempted to slow the airplane to stop the propeller, including cases where it happened in single engine airplanes.
Night, narrow canyon descending with questionable terrain clearance, attempting to slow the airplane and fly while concentrating on stopping the propeller is recipe for trouble. A better choice is to backtrack a little in the scenario, and make better choices that won't put one in that position to begin with.