That really depends on what classes you like to play. Questing will be a breeze almost regardless of your choice. If you're new to boxing, pick 1 melee char at most (for the main - its harder to control melee chars as slaves). If it was me, I would probably choose something that would blend easy with other classes for group scenarios. A priest/druid and 2 caster dps. Three locks would be fun too - and good for pvp as well, but might be harder to find a group with.

My suggestion: Go for 5 accounts and make 5 shammies or 1 priest 4 locks :P