The flat bottom floats will get up on step quicker and ride a little higher in the water, but in rough water they will pound the waves, where the vee bottom floats will cut through the waves better and probably track straighter. The general rule of thumb for height is the tops of the floats should be around 2-3 inches below the bottom of the prop arc. This will help in keeping the prop out of the water spray.
Seaplane