Duoing question.Follow

Meh... mage and priests work well together, especially if the mage is doing AOE grinding. I'd say, personally, that a melee class would work better with a mage (like a rogue, warrior, shaman), or a pet class (warlock or hunter). It'll be nice to have a healer so she can keep you alive (even nicer is she's shadow and will give you health & mana).

I have leveled a couple of characters with my wife and I'd say the best fit was Mage/Paladin because the pally could tank & heal. The mage sat back and nuked. That said, mage + priest should be able to blow through most quests just as 2 characters of any class can. Have fun with the wife and pick 2 toons you like to play. :-)

Pre-outlands, especially if you are a shadow priest, you'll gear fairly similarly. After that, you'll start to diverge. Then at 70, the gear choices will become even more distinct. If you're holy, there will be less overlap overall and none at all at "endgame" (defined here as anything you do after--ding! 70).