Here are some thoughts to help you brainstorm and decide what you like the most.

Synergy : classes that complement each other well
Having two of the same class means you may have less potential of overlapping abilities and buffs, such as two warriors who's buffing shouts don't stack at lower levels plus have a fairly short duration. A paladin tank and druid DPS means you have plenty of overlap: paladin benefits from the druid stat buff, and druid gets a mana regen buff. A warrior and mage combo means their buffs are pratically useless to each other. Don't overlook the special abilities outside of combat as part of the synergy, such as having two rez'ers in the group like Bot mentioned. I loved my mage for portals that made teleporting around the world so quick and easy, whereas a warlock's summoning ability is pretty useless to a group of 2. Shammies are a great synergy class, as it's almost impossible to have too many of them and provide more buffs/debuffs than any other class.

Versatility : have more options for progression
Hybrid classes give you the option to change your team structure more easily. A paladin and a druid means you potentially have the choice of 2 healers, 2 tanks, and 2 DPS without even having to re-roll, just a talent and gear respec. A mage and hunter means your hunter's pet will always be the tank, and the mage will always just be pure DPS.

Potential : can accomplish more
As already mentioned, a combination like a tank/healer would mean that there is very little that you can't do (including soloing instances at lower levels). If you went with let's say two priests, then you may own non-elites, but a single elite can be a bit of a workout and a group of them may mean certain death unless you master mind control or rotating fears.

Simplicity : less stuff to stress over in the long haul
The class combination of feral tank druid and resto/moonkin druid are going to share the same class quests, requiring less time running around on slow missions to unlock class abilities or acquire special items. A paladin and warlock combination will have one questing in Eastern Kingdoms, while the other one is supposed to head out to Barrens in Kalimdor. Simplicity also covers how easy it is to find groups for other things as well; there tends to be no shortage of DPS, but tanks and healers are almost always in demand.


There's probably a couple more categories you can add to the list here, but you'll find that while one group may be the most versatile in what you can do, they may also be the most complex to manage. Or one group that has the most potential of doing anything also has the drawback of having little synergy of abilities between them. So it's a balancing act of what you want the most out of the game.

My personal preferences are on potential and versatility. Any combination of paladin/druid/priest where you have one tank-class in the group is the most appealing to me as it gives me a lot of options at the cost of a simple respec. Plus, there's almost nothing I can't really do by myself. Some people like the challenge of trying to do more with classes that don't have it quite as easy, such as 5 warlocks, and have proven that they can do more than people tend to give them credit for. This is probably more thought into the question than you wanted, but hopefully helps you make up your own mind of how you want to play the game.