Everyone says this but almost no one succeeded to paste the "ribbons" on the 4 main classes without losing the archetypes.I've voted Ability scores (though, I'd thrown out ability scores and retained only modifiers), HP, Great Wheel and Levels. Also I'd add that progression should be drastic -- like from a human to a god.
As for classes, I'd return to Fighter, Magic User, Specialist and Cleric -- everything else can neatly fit as subclasses. I don't see any point in having Barbarian and Paladin as distinct classes, for example -- they are basically fighters, but with a bunch of extra ribbons.
If you paste Rage on a fighter, then it becomes an overpowered fighter. If you don't have the Rage, then I can't mechanically become a berserker. And balancing it with restrictions was never widely popular for long.