Doctor Archive

I have recently became a doctor and have wondered about the stimpacks. IF u have 3 stimpack C's, 1 Stimpack B and 5 stimpack A's how do u determine which stimpack is used in battle. I knw u could go to ur inventory and pick one but in the heat of battle no one has tiome to do tht does it go by order or striongest bcuz i dnt wanna waste a stimpack C on a 50/50 HA heal tht could easily be done by a stimpack A. Can u create a macro for this?