I don't believe there is one "best" spec and I usually swap between those three, mainly to test them and to vary a bit
http://db.vanillagaming.org/?talent#bxRhsVVoZrxxcc0V26/25, the mana pool is pretty handy for trash-healing and as a personal preference I enjoy having a huge manapool.
http://db.vanillagaming.org/?talent#bxRhsV0oZrxxcc0VxClassic 21/30. Not much to explain, it is the most balanced healing spec.
http://db.vanillagaming.org/?talent#bxrhsZfxtccMqx16/35, this one might actually be the "best" healing spec but it requires you to work with your fellow priests to ensure enough can buff spirit. The idea there is to get rid of -10% mana on cast which, while being a good talent, is not essential.
In the first two speccs, you are free to remove 1 point in Spiritual Healing to get Spirit of Redemption. While often an overlooked talent, I do think it has his uses, especially on progression. It won't happen often, but it could break or make a fight, and overall if you can help people stay alive longer, this is what you kinda need in progression.
If you find yourself dying often, I would consider moving 3/3 imp shield over the reduced threat (if you are horde obviously). This is not "better" but if you aggro less than your fellow healers, you might less die. Kind of a selfish PoV I am aware of that, but while you get warmed up to raid dynamics etc. it can definitely be helpful.
I've seen arguments over PoH. Well, you don't use that often but I think this is a really useful spell and validate the 16/35 spec. There is quite some situations where PoH becomes relevant (Huhuran's enrage, Anubisath Guardians in AQ20/40, poison bolts volley affecting the whole raid meaning your party can all lose 600-1200 HP, etc.).
I quite can't be sure how you can reach 9500 mana with full T2 without a flask. Are you alliance ? Doubt BoK would push you that far but it definitely helps.