I got 20 level 80 chars, and wont like to play only one of them. But if someone would force me, or if blizzard would say "M'kay, Multiboxers, it was fun, but.. No, bye", then i possibly would play my prot paladin as main.

Or my warrior.

Hm, no, one of my druids.

Nah. What about one of the priests?

Gosh. Good i dont need to chose only one. I surely would quit playing a little bit later because of frustration.