Bronze is nice and cheaper than stainless but the drawback is that bronze is difficult to weld so repairing any dings or what not may not work. If you primarily boat in shallow rivers where you run a chance of sucking shit up I would say spend the extra cash and get stainless because it can be repaired easily. Others have said that you can get away with aluminum with around 600 HP. Might be ok as long as you don't unload the pump. ??????