Gee, I think it depends on how much stuff you hit, and what kind of boat you have. In our shallow bay (sand and silt bottom), you will grind up an aluminum prop, with an 19' I/O runabout. The I/O weight causes the boat to dig in upon acceleration.
In that case a SS prop is better, as sand and silt have no effect on SS. Of course there are no rocks to hit, which is important, as hitting rocks with a SS prop will ruin the hub or destroy the gearcase, hopefully the former.
On our 21' OB powered boat, the boat does not dig in and hit bottom when accelerating. I use the Turning Point Hustler aluminum props. They have a high performance shape like the SS props, are about 1/4 of the price and hold up real well.