Also keep in mind that elite exp is higher and you can blaze through elites if you know what you are doing. The BEST exp is likely to be quests + instances of the right level.

Non elites are too slow to find, slow to respawn and give poor exp for a group.

If you were to optimize quests to only do the ones that were non collection, it would be possible that questing alone was faster - but I am not so convinced thats possible given that many steps of questlines require collections - which slow you down.