I like Master Airscrew for most applications above 8". I routinely overpower my planes somewhat, like using a .61 on a .40-size airframe, for instance, so wringing the last ounce of performance out of it isn't as important as realistic looks and safety to me. However, on .15 & under size airframes, I will only use Cox props...There simply are no more efficient props to be had. Some of the guys fool around with cut-down APCs and such, but you simply can't beat the thrust of a Cox out of the box...