The reason a single engine prop will drop one wing first is the prop wash. The wing where the prop is ascending will stall first because the prop wash increases the angle of attack on the wing (the part of the wing that is in the prop wash). On the descending side the prop wash decreases the AoA delaying the stall.
What I found about which wing would break first, usually had to do with the student or pilot being uncoordinated during approach to the stall. On your turn and bank indicator, ball out of center left, the right wing would break first, because it was skidding as you entered the stall. Ball out of center to the right, the left wing will break first, again, because you are skidding the aircraft as you approach the stall. Ailerons not centered will also affect which way the aircraft breaks during the stall.
This is why it is so, so important for any pilot, student or not, to work on slow flight in the aircraft which they normally fly. 5 Knots above stall speed, IAS, making coordinated turns in both directions, both with full flaps down and up will sharpen your pilot skills, so that anywhere in the slow flight realm, the pilot is always in control of the aircraft. Most single engine aircraft of today will recover from a stall by simply relaxing the back pressure on the control yoke or stick, and the aircraft will fly out of the stall.
The only time I could see the prop wash having any effect on which wing breaks first is doing takeoff and departure stalls, with full power, or full power, flaps down stalls, then I think it would be minimal at best, as there are many other factors affecting the aircraft during these type maneuvers.