Tier 4: Friendly Cooldowns
Choices: Hand of Purity, Unbreakable Spirit, Clemency
Hand of Purity protects against DoTs and other period effects. Unbreakable Spirit speeds up your big cooldowns. Clemency allows you to use your Hands more often.
My choice: Clemency
The big question in this tier is just what will Hand of Purity protect against. Depending on what effects the bosses have, Hand of Purity might turn out to be an amazing cooldown. But it might not either. Being able to double Hand of Sacrifice can be very useful in reducing tank damage. Not to mention being able to use a double Freedom to free two people from a root. Clemency is the more versatile option, but Hand of Purity may end up being more powerful on specific specific fights. Unbreakable Spirit isn't bad, it might allow you to get multiple uses of Lay On Hands, which is a lot of healing and mana back, if you don't need your Hands in that fight.
Tier 5: Throughput
Choices: Holy Avenger, Sanctified Wrath, Divine Purpose
Holy Avenger gives you the Ashbringer when you activate it. I'm pretty sure the other two can't top that.
More seriously, Holy Avenger would give you another throughput cooldown, It spikes Holy Radiance and Holy Shock by 30%, and allows you to cast more WoGs and LoDs. Very large amount of healing for minimal mana. Sanctified Wrath increases Avenging Wrath and allows you cast more Holy Shocks. Divine Purpose will give you 25% more WoGs, but spread out randomly.
My choice: Divine Purpose
The name of the game in early Mists is going to be mana conservation. Divine Purpose gives you more free heals over the course of a fight. Plus, it's one less button to press. Though the Ashbringer is quite tempting.
Tier 6: Damage and Healing Ability
Choices: Holy Prism, Light's Hammer, Execution Sentence
You only get this tier at level 90 in Mists, and I don't have any experience with these. So this is all just first glance.
Holy Prism is on a short enough CD that you can work it into your regular rotation if you want. Light's Hammer is great for stacked up AoE phases. Execution Sentence looks like a really strong tank healing spell that you can match up to boss specials. So I think this tier will really depend on what your role is in the fight.
Another aspect of Execution Sentence has is that you don't have to damage the mob. It's damage or healing. The other two are damage and healing. This may have important ramifications, especially if threat or crowd control are issues.
My choice: Execution Sentence
I don't really want another button in my regular rotation. I don't think that Light's Hammer will be really effective in 5-mans, because people will be spread out. We will run a lot of 5-mans in the early part of Mists. So Execution Sentence looks like the most useful choice, especially if we continue our traditional role of tank healer. But this tier will depend a lot on the specific fight.
This will be my standard build for Mists:
Pursuit of Justice
A lot of passives with a focus on tank healing. It should be solid for running 5-mans and tank healing in raids.
However, there are a lot of other viable choices, that you may prefer based on your playstyle and fights that you are working on. I think Blizzard has done an excellent job with the new talent system.