With the question being what's "best", more info would be helpful before a specific prop is given. What 91 motors- CMB 91HR's or 91RS's? Could even be OS 91's (yeah I know that's a stretch). What boat? What pipes & what lengths? What's the boat weigh? Are the motors worked over? All these are key factors in picking your optimum prop (quote- "Best octura and abc wheels to use?") especially on a twin. I'll agree that the Octura 1667 is one of the top props (and my personal favorite on twins) but the pitch/cup & diameter requirements for the "best" performing props can and will vary greatly depending on what you are working with. A pair of RS's will typically pull more pitch & diameter than a pair of HR's will but piped right the HR's may turn more top end. I watched a guy struggle to get a twin with stock 91HR's off the beach with 1667's but the boat went really, really well with a set of H48's on it and the pipes shortened. Sure there are probably a few different quick recommendations for an all around good running prop but for top ("best") performance all the little details will come into play. B)