I like to give it to those who I feel sync really well with me. Tanks who really do a good job at pulling big (Like a Paladin who will also know when to go into Shield Oath so I don't go through hell healing them), DPS who can keep up with their rotations very well and don't wind up swimming in AoE's (Especially if I see a Black Mage that can stay on their toes but still keep up with their high damage), and if I'm not healing I may give it to a Healer who can keep up with keeping us all alive while assisting in DPS if they can.

If I ever see newbies/sprouts who do really well in my eyes, I'll also give it to them.