I'm very laid back about commendations and I just go off a flow chart I thought up:
(If I'm a tank) - Healer if they both dps and heal adequately.
(If I'm the healer) - Tank if they're consistent with pulls and use CDs. They don't have to be a fast puller, however they can't pause 30 seconds before every pack of enemies.
(If I'm a DPS) - If the other DPS has, well, good DPS.
(If there's a cool or elegant looking Elezen) they get automatically, unless they're a jerk :V.