"The two styles serve differen
"The two styles serve different puroposes, so it depends how you use the boat.
A 3 blade will ultimately give you better top end performance - not so much that you will really notice, but could see a couple more mph at wide open.
The 4 blade will get you out of the hole faster, get you on plane sooner and keep you there at a lower speed than a 3 blade will.
So if you use the boat to tow ski's, tubes, boards or do alot of cruising or travel distances in "no wake" or reduced speed areas (canals etc), then the 4 blade is the better choice.
For just general "horsing around", the 3 blade can be considered a "standard" prop.
Since you are running a 4 blade you would normally move up in pitch by 1" going to a 3 blade of similar characteristics (same diameter, same material ie. stainless, or whatever, cupped or not cupped).
However, if you were running say a 19 pitch 4 blade aluminum (non cupped) moving the a 3 blade stainless would probably stay at 19 pitch since the stainless flexs a little less/bites a little harder than aluminum or composite.
Selecting a prop is a bit of trial and error with a little bit of science thrown in..."