Well, depends.
I tend to go with, depending on campaign type and expected length;
Three: Fighter, Magician, Specialist
Seven: Fighter, Magician, Cleric, Rogue, Druid, Spellsword, Monk
Twelve: Assassin, Bard, Cleric, Druid, Fighter, Magician, Monk, Ranger, Rogue, Paladin, Sorcerer, Spellsword