I rarely give comms to the healer because they usually get it without even trying. I've played all 3 healing jobs to 80 and honestly its the easiest way to get comms... I recently levelled a Pally all the way to 80 and I barely got any - tanking is often an underestimated job.

Now? I either give comms to either the tank or DPS, depending who I thought really made a difference.