Two things come to mind here. One, the feel and action of the brake shifter hoods between the two. I would base my decision on that. You either prefer double tap or you prefer the twin lever fully moving brake lever of Shimano. For me, being a Campy use, I don't like the way that you have to release the shifter levers to fully realize the shift. It's like click-click. With Campy, pushing either the brifter or thumb button activates the shift and all the release does is to reset the ratchet. Shift made. When I ride a Shimano bike, I never get use to the fact that you have to fully release the lever for the shift to take place. SRAM users can educate me if this is the case with their group as well.