Hey, my guild and I have been running Gara'Jal the Spiritbinder 10man.
We are 3 healing it, and I am a Resto Shaman.
I can't for the life of me figure out why the other 2 heals can get their Spiritual Innervation on the dps up to 22 or so, but when I go in I can only get up to 8-10.
When I get into the spirit realm, I immediately drop my Healing Tide Totem, use my Ascendance spell which doubles all of my heals, then I heal us all up to full with Healing Surge, I Riptide one of the dps, and then spam either Greater Healing Wave or Healing Surge until the last possible moment. I am seeing healing crits pop for like 150k, but when we leave, the dps only have 8-10 stacks.
At this point I'm pretty sure you wont be able to beat enrange running 3 heals, We nromaly have or resto shammy go ele and then drop healing rain for the final burn phase to help out. as for 2 heal strat the amount of stacks u get doesn't matter all you need to do is to make sure everyone has their exit button, and then leave asap to assits the solo healer out in the real world.
This is from a Shadowpriest PoV, as I haven't healed the encounter yet, but this has been my understanding. We initially thought it was based on the amount healed, so our healers were dropping their biggest heals - we were getting 6-9% stacks, on average. Then we switched from large heals to flash heals, and stacks came in around 12. HoT healers are at a bit of a disadvantage, as we noticed you get 1 stack per HoT cast and not per tick.
On every other Spirit Totem, I go in with 1 other DPS (usually a Boomkin). He DoTs everything in sight, I hit Halo, throw some VT for mana, and then I spend the next 15 seconds spamming Binding Heal. This gets us both 22-24% with ease, and our healer, if one needs mana, can focus on his own stacks.
Switching it up with sending in a strong hybrid to help boost stacks took us from enrage @ 2%, to clearing 'serk by a good 25+ seconds.
So I guess, long story short, use direct heals whenever possible, and I'd default to the fastest, but you can certainly experiment.
EDIT: Regarding the size of the heal, we did notice that our Pally's LoH, when cast on our Hunter was giving 8% stacks every time. Other than that though, we typically found that Flash heals, put out more stacks than Greater Heals. This may depend on spec, but with a Disc and HPally, healing, and a SPriest and Boomkin boosting heals as well, quicker was better.