It all depends on what you want from your prop. If you want the higher top speed and performance go with the stainless. If you don't mind sacraficing a few mile an hour go with the aluminum. They may break easier, but for the price of a stainless you can buy 2 or 3 aluminum props and keep a spare onboard. If you do hit bottom you want the flex of the aluminum or it can get very expensive (speaking from experience).

Jim