What boat you have is irrelevant. tell us what motor(s) you have and we'll help.
If your engine/engines is/are rated for use with the 87 octane, then this would be a far better choice considering the non-ethanol base. Higher octane does you no good if the lower octane is correct for your engine. Higher octane does not make more power (if the engine is rated/set to run on a lower octane fuel) and is not cleaner or better fuel. In fact, if an engine is tuned to run on 87 octane and you run a higher octane, you can actually reduce the performance ..... unless the engine management system incorporates knock sensors AND the system is capable of adding more ignition timing advance, over what it normaly runs when 87 octane is used.
Ethanol fuel loses octane very quickly...in a matter of weeks. I would buy ethanol free gas for as long as it is available. Most marina fuels have stabilizers and carbon guards etc in it so they last over a year and are better for your engine and ethanol free but cost more $$. I think it is worth the $$.
I concur with both bigshot and M3EATER. As for the cost difference between marina fuel and gas station fuel--you'll be adding stabilizer to gas station fuel, effectively upping your price per gallon. So the difference isnt as great as it first appears.(besides the convenience if you dont trailer your boat)
Use the higher octane and Startron, the higher octane will give you a better running motor.