
My main is an 80 Priest (disc/Holy Dual Spec)
I leveled her from 1-72 as holy and from 72-80 as shadow (simply because i didn't have my usual questing partner, my boyfriend during nrend, and also because its harder to grind instances in nrend as well.) I pretty much instanced grinded until 70. I only quested when I had a friend to follow around and healbot. Call it lazy, i just don't have the attention span to questgrind like crazy. + I like instancing. Even though everyone tells you (and for the most part its true) that questing is the way to go. I just chose not too. But, there were some added benefits for this. Pre Wotlk: Doing all the outland instances by the time i hit 70 i was already decently geared, + i had the rep to do heroics immediately, and third I had TONS of experience healing 5 mans which GREATLY prepared me for kara IMHO.
if you say that you have a friend that you quest with
just dot up/wand if necessary
and heal your friend.
if you're going to be soloing a lot i would recomend shadow (even though i never touched shadow.) or at least get spirit tap and go disc.
As for mana efficiency, yeah
until you get some epics and a nice bit of intellect you're going to have mana problems.
ESPECIALLY as holy. I was holy for MOST of my healing raids career, and before i knew how to manage my casts I would go OOM every boss fight almost. I eventually tweaked my healing style and didn't have much problems until ulduar. Then I decided to research Disc and try it out.
If you go DISCIPLINE you will pretty much NEVER run OOM. its honestly sad. That is my Mainspec. Pve Disc heals. (aka cloth pally heals, lawl.)
And with the damage mitigation, + regen talents + regen from int its sad how much mana i have at the end of each fight(while thoroughly keeping the tank up and tossing raid heals as well)
As for shadow
I don't think priests should be shadow. Everyonce in a while i will find a SUPERB shadowpriest. but its rare. I don't think they are great dps, the only thing i like about shadow is the mana regen for raids (i would never be shadow but i don't mind having a shadow priest around me hehe.)
You could also check out Elitestjerks.com on their priest stuff.
Anyways I hope I helped. I'm super passionate about my priest and I love priest heals over most every other heals. (i've played paladin, shaman and druid heals as well.)
Don't forget to utilize everything you have!
A lot of priests forget what they are given, for instance, priest healers dying cause they couldn't heal themselves while keeping someone up. this makes me sad cause 9/10 times this can be solved by Binding heal. also although its a 10 minute cooldown, Divine hymn is TITS. its great for raids.
EDIT:
I also agree with everyone though, Priests are a difficult class to level. Especially if you are holy/disc. It does take an experienced and patient player to do it.
My hunter was probably the easiest to level. I didn't do s**t. then when i got to kara i would just autoshoot bosses and get food/drink/go to ladies room when necessary. No one ever noticed! lawlz! and i was still like 3 on dps for that specific boss from JUST autoshoot. My paladin was also easy to level. I went prot at first and got her to like 40. then i just decided to go ret idk why. after going ret it was stupid easy to do s**t. My paladin could kill ANY ALLIANCE pre 80. she killed 79's when she was like 72. She was ALWAYS 1 on dps in instances even when there were people that are still epic'd from level 70.(she wasn't. i leveled her after wotlk.) Shaman was difficult. Not extremely difficult but harder than pally and hunter. My warlock was relatively easy.
OK. i will stfu now. lolz.

