There are a lot of different aspects to healing... first your mana pool describes how long you can heal for, and your mana pool is determined by your raw mana pool + regen + HPM of the spells you cast.
However just being the most effecient healer doesnt help much if you don't have the raw power to keep up with incomming damage, and this is measured by HPS. At the end of the day a target will take damage that can be described in DPS and the healer will need to be able to provide the same or better HPS to keep that target alive.
Obioviously healers need to balance their mana pool with their HPS ability to keep people alive. What i'm trying to illustrated is that crit has very little effect on HPS but has a great effect on mana pool. Its obvious that some people in this thread are either too stubborn or too stupid to acknowledge that fact. Instead they just make some sort of logical connection that because a crit heal does 50% more healing it must increase your HPS... it can but its so small to basically be insignficant.