Harrison I'm sure you have seen him enough by now.
Kudla- Very good baseliner, backhand is the stronger side and he has good movement. Really nice potential.
Sock- More raw as he has only been pro for a short time, but he has a very good serve and heavy attacking forehand. Good at the net, also. Needs to improve his backhand and movement.
Kosakowski- Only one of the group with a 1 handed backhand. Decent but nothing stands out.
Collarini- Haven't watched him too much but he's a left handed claycourter in the mold of so many other similar players.
So this must be one of the reasons why he was chosen as DC practice partner against Switzerland.