Looking for some discussion on how other healers prefer to socket and the thought behind their choices.

I've pretty much gone for regen and +heal, but am recently considering going +18s in just about all my sockets and bypassing the mp5. With raid buffs and average healing gear now I'm hitting +1670ish and 420 Regen (205 in combat). I should have my whitemend set in the next couple of days and the regen on those wouold off-set me resocketing to keep me at about the same regen as I am now but could significantly increase my overall +heal if I go for all +18s.

Might want to check out this thread on balancing healing and regen. Gems are really the only place where we make this choice in a vacuum, so the thread will pretty much sum up the relevant issues.

205 in-combat regen (assuming that's unbuffed) is a pretty solid number. At that point your +healing could probably stand a boost, though all +healing gems might be a little much as there's no real downside to regen. The nice thing about being a Priest or Druid is the option to use spirit gems as well as mp5...personally as a Resto Shaman I use all Royal Nightseye, all the time unless there's some really compelling set bonus I'm going for. My reasoning is that +healing and mp5 are by far my most important stats, and Royal Nightseye offers more of both than any other gem. It's that simple.

Speaking from my own experience with raiding Priests though, they tend to run short on Stamina and get incidentally killed a lot because of it. Slotting 12 Stam here and there is definitely something I'd recommend.

That's a good point, particularly if you're rocking the common no-stam Primal Mooncloth/Whitemend combo. I put stam gems in my blue sockets on those pieces, which makes them still be the strongest heal/MP5 pieces in their tier, but also makes them wearable in fights with incidental damage.

This is what i've been going over in my head to try and come to some sort of conclusion.

This is all very situational, but what isn't in this game?

In my experience as a healing priest is there are three basic healing 'roles' that I could be put into in any particular encounter.

5-mans - need strong +heal for the heavy damage, mana regen has never been an issue in any heroic I've done as I've yet to go oom. The winner in this situation without question in +healing

25-mans - Here i'm either OT or MT healing, and on the rare occasion raid healing. When I'm constantly spam/cancel healing, the more +healing I have allows for lower ranked heals that in turn conserve mana. In these situations its rarely the ammount I heal that matters, but the fact that I'm able to sustain the spam/cancel healing for 10 min if needed. I guess you could argue either the +heal to allow lower ranked healing or mp5 to keep you going longer and that both could in theory accomplish the task.

So, when looking at those scenarios is seems like pure +healing might be better in my situation.

When you're trying to get "max HP healed over X time taking mana into consideration" there would be a certain breakpoint of X healing = Y mp5 = Z spi depending on fight length, time in 5SR and the buffs you have (and obviously your class and spells used). It's not that hard to calculate, calculate how much of each "mana stat" is needed for 1% increase in mana pool, how much +healing is needed for 1% increase in mana efficiency and for stats that gives both (aka spirit for priest, int for pally), check what's the needed amount for combined 1% when you add up the % increase to mana and % increase to heals.

The problems start when you actually have more mana than you need. We all know mana left at the end is useless, but so is overhealing. At the end the only difference between more +healing and more +mana in equal amounts is that the +healing allows for increasing your max HP/s, while mana doesn't, which means with the above calculation when it's even between the healing and regen, in reality the healing is always better than what was calculated with the method above. However that only means that the breakpoint is somewhere else, requiring more mana to equate that amount of +healing. Problem is that breakpoint is extremely dependant on how much you would gain from maximizing the HP healed over time taking mana into account, VS maxing your HP/s.

Doing the calculation mentioned in the 1st paragraph is really the easy part, which is pretty much what lots of people are saying on this thread (like "the more +healing I have allows for lower ranked heals that in turn conserve mana." or "the more +healing the more hp/mana I get but more mana gives same effect").