What is your preference for a player to get a commendation?

[Voltyblast]

As a tank, I usually commend the healer (especially when they heal me through a big pull or a bad pull by mistake)

As a dps, I usually commend the tank for keeping the aggro (I'm a blm)

As a healer, I usually commend the tank or the dps, depending on the situation (deaths, survivability, etc)

Can be exception, but this is my general mindset.

Also, words and chats or greetings doesn't automatically make commend-worthy: I learned that just because they say hi, it doesn't automatically mean they're nice. That's experience from life itself.