I'm gonna have to cheat on Priest healing since mine isn't 70 yet.
Here is an excellent guide on how to heal as a Priest:
http://elitistjerks.com/f31/t17086-priest_holy_raiding_compendium_2_3_x/I suggest all Priests and wannabe Priests read that whole thing.
BTW, the answer is Greater Heal. It's supplemented by lower ranks of GH, Prayer of Mending, Renew, and very occasionally, PW:Shield. No Flash Heal! Flash Heal is basically the lazy man's crappy heal. Use it when you don't care at all about losing mana or people dieing because of you.
This post is just to tide me over so that I can think more about what to put in my upcoming Paladin Tanking post.