Depends on the hp lost by the whole party and by the amount of aoes being dished out through the fight. If its something like t12 phase 3, yea some medica II > I rotation might be in order but if its something like vault last boss a simple medica II > pick up those with least mp with cure I and then go back to tank with a freecure proc saves a lot more mp than simple medica I spam for the exact same job.
It's all a matter of knowing how much damage is being dealt and how potent your own healing is and heal accordingly.
