Basically....proper pitched aluminum props are designed for general use, and cost effective, most motors under 109 up use them unless your running for optimal performance. Then the SS props come into play. Usually used for performance type motors. They do stand up Vetter to sand and other abrasive lake bottoms that would wear an aluminum props quickly. SS props are expensive at 3-4 times the cost of an aluminum prop. The aluminum prop, while it can be repaired, they are also considered disposible. S S props can be fine tuned for optimal performance, blades are thinner and stronger, but the downside is...you can do a lot of damage to your engine if a rock is hit and the stronger SS does not give way like an aluminum prop.
Bottom line is.....how much are you willing to spend to get the last ounce of performance from your boat and motor, and how much abrasive stuff are you running your prop thru on each outing. Those who don't need every mph availiable, and are cost concerned or don't have abrasive issues will choose an aluminum prop. Consider what you are going to do with your boat and how much performance you really need. Nothing right or wrong with your choice and it is your money your spending.