My wife plays a shadow priest with my paladin. Near Lv60 and earlier I was Ret spec. Once we hit the outlands I spec'd prot to help with dungeon runs (very few prot specs pre-70 on my server).
For leveling? Go ret + shadow, you will kill almost instantly and only get stronger. Stock up on good drinks and go to town. Being that your still a paladin you will both handle any "ohh crap" moments with ease. Doesn't matter what spec you are.
If you want to run dungeons duo? Go prot & have him go Holy. Never plan to tank AND heal, its not gonna happen. And don't expect the priest to tank elites >.> To stay effective take advantage of Spiritual Attunement and Judgement of the Crusader. A holy priest with a few +spell damage stats can nuke just fine with Crusader judged.
Looking for groups? Either or works. With the right gear set you can heal, DPS and tank as any spec at those levels. Just dont expect to be top of your class. (from above) I went prot because we had very tough times getting good tanks, and we were getting into some tough runs (slave pens, underbog, ect.).
Plus I figured "duo" questing would still be easy... because that's what I've always read... "prot can AOE grind, blah, blah... FYI: I'm not a fan of this.
Does it work? yes, but;
For ONE: who "grinds" much anyways? questing seems much more effective with building finances & easy gear sets. Now.. for Rep? sure, I'm cool with that... but I'm guessing most don't spec to grind rep unless they are already Lv70 >.> just a hunch.
For SECOND: AOE grinding requires "special" set-ups. You need to find spots with melee MOBs that are fairly close to each other (something like the Raptors in Un'goro) and round them up. Then go to town, drink up and repeat. Sounds easy.. efficient... fun... until you realize the 5-7 MOBs you just killed took 5min+ and now have someone else there killing them also, so your "big" pulls are limited. Or you cleaned house and have to mount up to find more before the MOBs you killed "all at once" pretty much re-spawn "all at once". Don't get me wrong, many like it.. I do not, just my preference and going prot to find questing is very slow had me missing ret.
For duo questing as Shadow + Prot pally = mana gone. Bring lots of drinks & INT gear, you will not take enough damage to have your small mana pool refilled. Saving quest +INT gear is very helpful because HPs while questing isn't as important as low down time. You will find yourself very very rarely getting close to 1-shot, and if you do; don't go back... ever... even for your body, you are NOT supposed to be there. Or try to avoid agro'n that skull elite again. Close to death spots either look for help, or equip your tank gear and try that.
Holy + Shadow? same as Ret except much slower... Holy is nice, I liked it when I was Holy, but for leveling IMO Ret is the way to go. Pair that with a shadow priest and go to town, you'll love the "I'm going to kill it before you can touch it!!" wars you'll be having =)
Edited, Feb 18th 2008 5:34pm by Killzon