I always give to the dps if I'm playing dps. I give it to the healer if I'm tank and vice versa. I only deviate from this occasionally. I will automatically not comm a bard/mch for not using foes/mch foes if I'm on my black mage. Same goes to a nin if they don't goad and I'm playing some tp based dps and we're aoeing a lot. Otherwise you have to perform pretty badly for me not to follow my usual comm priority.