Since the shoulders are so similar (the non-tier have an extra socket, but isame itemization so it's not a huge difference), I think it just comes down to the chestpieces. Here is the comparison.
So, 108 haste and an extra socket, versus 100 spirit and a little crit and the 10% boost to CoH.
I'm torn. 10% on my favorite AoE heal is a lot, but so is 108 haste (I'm low on haste, currently at 900-ish even with MCR on and a lot of haste gems). And the bonus can be largely overheal with the lol30% buff.
What would you wear?
If it helps you decide, I'm just coming back to WoW after a few months - my guild has progressed to 8/12 H 25 (I've never been past 10/12 reg 25, and H Lootship of course). I don't remember the exact healing comp, but we have two Holy Pallies and a Disc Priest for sure. The rest is a smattering of Resto Druids/Shammies - I know I'm the only Holy Priest in the guild atm. (I believe "smattering" is the technical term)
I can't remember ever having mana issues, not since I got into 251/264 gear. And if I somehow do, there are Innervates available, and I have a few pieces that I can swap out - I have Dying Light gemmed with int, for example.
Any other gear/spec/whatever advice is always welcome.