I'm weird I guess and use Echo from this tier, because of its increased proc chance from Chain Heal, which is my primary healing spell for most 25-player content. I do use Elemental Mastery for a few fights - Lei Shi (I alternate EM/Ascendance/SWG for one Get Away! phase and Spirit Link Totem/Healing Tide Totem for another), Tsulong, and currently giving it a go for H Sha for more cooldowns to cover Huddle in Fear healing.
I also play around with staggering cooldowns vs popping them all together for various fights. I mean, sure, if I popped all my CDs together to heal the first Force and Verve on Imperial Vizier Zor'lok, I would do amazing healing, but then for the later FnVs, we may lose people, and I'd have nothing for that. I'd rather do worse on the meters but better at my actual job of keeping people alive by splitting my CDs up and being able to cover every mechanic with something. Meanwhile, on Tsulong, if I didn't pop all my CDs while Tsulong had Guardian Spirit up, I'd be crazy.
I don't think there is a single right answer, I guess - not to which Talent to take, nor to how to use it. Healing isn't like DPS where you can just math out a Talent and find that one has a 0.6% increase over the other so that's clearly the one you take and you use it on CD. You really need to consider the fight mechanics, the abilities of the other healers on your team, and how often your group may make use of hybrid healing/damage reduction cooldowns in order to choose the right Talent and healing style for your raid on each encounter.
Fortunately for you, it's cheap to change Talents! So while I do think AS is more generally applicable for 10-player content, you can give EM a go and see if you like what it does for your throughput/ability to cover threatening mechanics - and if you can live without the instant tank emergency heal or the instant HR during Ascendance - and decide for yourself :)