One versus them all

We've seen Paladins soloing some crazy things, but player Parvati of the Zangarmarsh server wants to know what class would be best to solo pre-BC high level instances.

I suppose it would depend on the instance. Druids can stealth past a great deal of Black Rock Depths trash to get to the bosses that drop the good loot. But a Paladin would do better in Stratholme. And Hunters can go just about anywhere.

Parvati doesn't give his motives behind the question, but cash farming sounds like the obvious motive. But why restrict yourself to old world zones if that's the case? Cash is far more free flowing in the Outlands.

Whatever his motive, I would like to hear what you think. Not just what class, but why.