[Brandon Ha]

I suggest you take a look at a Simbotics Seminar. Specifically, the Running a FRC Team episode. (Near 40 minutes) Karthik does a stellar job of detailing how the decision should be made and what things to look for in such a student.

Personally, if I had to make a decision for the drivers, my criteria as the coach would be
#1 Can I work with this person.
If your team cant stand you yelling and screaming at them and understand that it is because you want them to succeed and maybe it was a little loud or you wanted to be clear with them.
#2 How will they conduct themselves with the team and the game.
Your team has to have balls of steels and push everything to the edge of failure. One personal example is in 2012 for my team. Our driver needs to get up onto the bridge and balance. Arm mechanism doesn't work, alliance doesn't have another method. What he does is he uses the high COG and "rocks" the robot to lift our front wheels up and onto the bridge... That is not how the team built nor designed it but he pushed the edge and succeeded.
The other part is how they conduct themselves. Are they gracious professionals? Do they win as an alliance and lose as a team? What about their communication skills. Can they talk with others to tell or fix the issues. We do not want to go onto the field and wait for 5 minutes to find out that they forgot to put a battery in. This is the easiest part because you can make them take a clipboard with what to do every single match or teach them beforehand.