For my healers should I change to Endurance instead?.
Lolwut? Healers shouldn't be using Endurance crystals. The only class that has any reasonable excuse to do so is Tanks and, even then, only if they explicitly need the hp provided by it.
Most people use Power crystals for all of their characters when they can, but that's because, at 50, most people have all of the crit rating they need through mods and enhs. While leveling, it doesn't really matter and you can just focus on getting the best crystal you can.