Why tank again? Noones talking about the tank.

2 players got hit by around 2k damage and stand close enough -> Cure III wins in MP cost and GCDs used against 2xCure II, medica will not be enough, if you need those 2 players full asap for whatever reason.
With more than 2 players close enough it gets a no brainer.

If theres more players to heal at a greater range than Cure III can offer, of course you're not using Cure III.