One of the great joys of WoW is how couple-friendly it is. My wife and I are suckers for some cooperative multiplayer, and we haven't looked back since we set up her account. We play together all the time, doing dailies, farming mobs, instancing and raiding (although we're learning that being new parents isn't really conducive to raiding, so that's trailing off). Also, leveling alts.
We have some experience leveling a number of duos.
Druid and Rogue
You want to see two great tastes that taste great together!
The primary bear druid move to generate threat puts an effect on that increases bleed damage. (Hey, rogues have bleed damage!) One of the rogue's primary abilities is to stealth. (Hey, druids can stealth too!). If you don't feel like killing through to a named mob to finish a quest, you just stealth by them. Vanish plus travel form means that you can both easily escape a fight that goes south. Druids can dps, tank, or heal, so you can change the makeup of your tandem at will. You can even go and duo instances by skipping mobs. This is the strongest tandem I've seen in the game, it's really fun to play.
Paladin and Mage/Warlock
Aoe tanking, meet aoe damage.
Pally runs in and introduces himself to fifty people, starts shaking hands and smiling. Mage/Warlock takes all their information down and rakes in the campaign contributions. Both are elected to max level soon after.
"Go kill X critters" quests takes on a whole new meaning with this combo. "Whee! Let's go find X critters!"
Melee and Healer
In my case, this was Rogue and Holy Priest.
Rogues can kill pretty fast. Healers, well, enable rogues not have to stop killing… ever. One of the sublime joys is enabling my rogue wife to just go on a tear through whatever content or mobs she wants without slowing down. Obviously, one of you has to get joy from healing for this to work. Luckily, I have an incurable fascination with healing, so we're golden.
(Melee works better than nukers because melee damage doesn't suffer from spell pushback. Nukers have to finish fights before they start getting hit, for the most part. And in that case, why do you need a healer?)
Hunter/Warlock and Pet
Honestly though, it is kind of weird when people start talking about their in-game pet by name, with obvious emotion in their words. I understand that your pet was with you through thick and thin as you leveled up, but that doesn't make it a toon of its own.
Raid Lead: "Hey everyone, welcome to our guild's first Karazhan."
Hunter: "Me and Fluffy the raptor like Karazhan so far!"
- Secret Design of WoW PvE: Solo Performer vs Group Utility
- WoW Wrath Class Redesign and Reitemization Explained
- Secret Design of WoW PvE: Your role in a PvE raid
- WoW Itemization Dreams
- Secret Design of WoW PvE: Variety vs Specialization