It really just depends.
Some comps require different orders for you to try out.
We usually go for 1-2 healers first then the dps. Healers just gotta be able to heal though, use CDs, cleanse, while others CC through their dps.
We did try DPS first in one time, needed massive priest dispels to get rid of the resto druid hots to burn through the dps.
But again, it all depends on their comp, your comp, and adapt.