First of all, If you called them "dink" floats in Canada they would laugh at you. Believe me, It happened to me.
i like the 5.5 to 6 inche ones with 2 holes. I also use the center hole style for steelhead on occasion.
Black is a good color, but white is even better. Look at a fish, darker colors on its back lghter colors on its belly. white doesnt contrast against the surface (looking up) as much as black or grey. As for the very top color, Orange or chartruese is good.