The most important rule for being a healer is do what you want/ think is best.
If you keep ppl up without stealing aggro etc then by all means do whatever. You can do all the math u want but at the end of the instance the only thing that mattered was if ppl were healed or not.
Anyways imo:
Cure 3= a cure 2 medica it's like ur using cure 2 on everyone.
It has faster cast time than medica 1/2
Medica 1= when ppl r spread out and there's little damage incoming / sustained.
It's like cure 1s for everyone.
Tbh i actually haven't used medica 1 in a lonnnnng time.
It was always divine seal + medica 2 & regen or just cure 3 with DS or PoM.