Aluminum may be a safer bet in the river. Having said; the majority of owners that I know, run SS props on the river. I asked that question to the marina, and they said the difference in performance between the modern Aluminum matrix props and SS is negligible.
If that’s true, I will probably stick with Aluminum for cost and its ability to inflict less lower unit damage if I strike anything underwater.
Merc recommends a 17″ pitch for the standard Merc on my boat. Interesting, because I ran either a 19P or 21P on my two stroke. I preferred the performance of the 21P.
I don’t think hole shot will suffer with the command thrust… so maybe best to go 3 blade for a bit more top end?

bigcrappie
The command thrust has the same lower as the 150. Its sturdier and will last longer. It also provides and incredible hole shot due to gearing.
I am not concerned with the prop for hole shot, looking more for top end.
The CT will provide plenty of hole shot on its own.
Good point about the 3 blade… that might be a better option in this case.

I don’t really want the spice though…