Best Duo - Level 15 and under.

[Bubbles]

Mage
Necro
Druid.

Druid probably the most popular choice since it's such an incredible fear-kiting combo.. But honestly, there isn't nearly as much content to fear-kite in classic that's worth the time and effort. The real joy of druid is the regen/heal aspect, along with the porting (which is always great to have).

Since you're looking at more of a likely-balanced style, with plenty of dungeon crawls and exploring, Mage/Necro or Necro/Necro would go a long way. A druid simply doesnt add much in close quarters compared to the other two combos.

The mage DS + Pet + DD + heals adds incredible dps and survivability.. And two necros can heal and mez and undead lull and root and split camps and pretty much do anything they want with little to no real risk. (3 cheers for Feign Death)

Also, considering the evil nature of the necro, you may want to consider other aspects when making your choice, such as making the mage a good race, etc for selling abiities (druid even easier since they can be loaded up and simple bind, port to a ring, and gate back, etc.

But yeah, above all else, if you get past the redundancy, it's darn near impossible to kill a pair of necros in most situations. And when starting from scratch, pet casters are very easy to gear up AND require very little gear to begin with.