I am going to try and get back into WoW, and I think I am going to roll a Priest. I am sure its not a huge difference while leveling but which spec would be better while "leveling" through LFG? Currently I am Disc, I've went Fiend and BnS only level 36 right now.
Disc. You can queue as DPS or Healer and will do pretty much the same DPS as Shadow (if not more), and heal the group when needed. If you're DPS, you also help the healer heal passively (you will get Atonement at level 38)... Win-win at low levels!
I leveled as holy dps. Chakra really helps your dmg. Shadow spec will outdps holy/disc after 70+ i guess.
Both holy and disc priests do high amount of dmg and lets you heal just as much. I just chose holy because of chakra looks badass :P
Oh yes, if you're leveling in dungeons almost exclusively I'd recommend discipline. I leveled a second priest and tried shadow for awhile since my main was disc/holy for the longest time and found that mobs in low level dungeons just die way too fast for you to even get much damage on them since you're counting mostly on your dots.
Once I went discipline and got atonement I could outdps all of the other members of the group all the while healing them up until Cataclysm dungeons. It was also a fresh character on a fresh server so I only got heirloom items you could buy from the guild vendor after joining a friend's level 25 guild and borrowing some gold to buy them.
I honestly think holy is superior to disc for lowbie instances (and higher if you have the gear for it). You will deal more damage as holy if you don't have to spend a significant amount of time healing, and in most low level dungeons a hierloom tank won't even take any damage, you will also be way quicker outside of dungeons as holy. Either way I'd say that priest healing specs are amazing for instance leveling though.