For leveling it's CotA nothing else even comes close to comparing the experience you get in here from killing the white mobs.
For legendary items, Core of Arreat chest farming.
So what is a solution and what would prevent this in the future?
For a start instead of manually doing each zone with chests and enemies and instead of experience being the way it is, why not have the dps and toughness of enemies effect not only their experience amount but their drop rate? This would make elites give more experience than whites and would be worth killing. It would also prevent certain areas being much better than others (some disparity would happen).
Now to make sure it's not unbalanced have an experience amount / enemy amount per zonal area, what I mean is say in a 100 x 100 yards are you can have either 20 basic enemies, 10 more powerful enemies (or a mix of them) or an elite pack, this would do a number of things but in general it would make sure mob density is good everywhere, it would make sure expereince gain is good everywhere and drop rates wouldn't be damaged.
Now chests 1 chest per 100 x 100 yard square or even every 3 or 4 or whatever but make it so it's balanced across all zones.
Your thoughts people?