I can tell you more than you want to know. Best to have more than one prop, it you can do it, for different usages. BTW, always, always carry a spare everything (prop, nut, hub, thrust washer, etcetera)
The real question is where are you going to use your boat. If you're going to be offshore 75% of the time, go with a stainless, and you'll probably need about an 18" or 19" pitch in a Mirage Plus or PowerTech Offshore 3-blade. By contrast, a 4-blade will get you on plane faster with less bow-lift and with better maneuverability, but at the cost of top speed and a slight hit in fuel economy at identical speeds.
Here's the target: You want to be able to hit maximum rpms when your boat is at max gross weight.
Almost every dealer will want to prop your boat to hit max rpms at minimal load. That way he can show you how fast and maneuverable his engine makes your boat seem at speed.
So here's what happens next: On the day you set out for a full day of fishing with a full load of fuel, and a full load of food and drinks, a full load of bait in the full livewell, and a full load of fishing idiots, er.. fishing buddies, you'll swear somethings wrong with your motor, cause it struggles to get the boat on plane, and then performs sluggishly. In those cases, it's not the boat or motor, it's the loose nut behind the wheel who has the wrong prop on the boat for how he's using it. I have a 90 hp Optimax on my Seafari, and I have a stainless prop, and a composite prop, AND an emergency get-me-home prop.
If you do most of your boating in very shallow water with rocks, reefs or shoals abundant, aluminum or composite construction is generally better. The exception is if you run a Hydro-Shield or a similar similar prop protector, in which case stainless is fine.
I live in Citrus County, Florida, where the coastal area are very shallow and predominantly made of oyster bars and small reefs. I run a stainless prop for the performance most of the time, but I also have the above-mentioned Hydro-Shield. I ran aground one night on an oyster bar at about 25 mph, and ended up hull aslant, but my prop was fine, as was my lower unit and prop shaft. No damage apart from my pride and my bottom paint. I had to wait over an hour for the tide to re-float my boat to where I could walk my boat off off the bar.
