Grubbs has the better throwing mechanics, Hart has a slightly stronger arm, but neither is lacking in the other area.
Both can make all of the throws to all areas of the field, and both have great field vision.
Two things might have swayed Hart away. One of them is the very hard push that Louisville is making, and the other was probably when his Cocoa teammate Jayvan Boggs took us out of his final four. The two of them are close friends, and it would be understandable that he'd want his favorite target on his team.