I know that this has been beat to death but there really never seems to be a definative answer. What works best on an Agressor with around 500 hp.???? 3-blade or 4-blade.

A 4 blade

I think it depends on the x dimension, and if the bottom has been altered. I have a '97 that has the hook removed with a 2" shortened Imco and I have to run a Bravo 4 blade. My fastest prop is a Hydromotive, but I have trouble getting on plane and it does not cruise well at all, so I stick with the Bravo. Before the changes my best prop was the Mirage (but I also had less HP then )