On double xp day, you can level 1-71 in less than 2 hours. Maximum elixirs/bonuses required.

Very very very easy. 71-81, cumulative game time of less than a few hours per day, for 1-2 weeks. Dependent on how far you got on double xp day. Dailies are most efficient. If you have the plat/gold to sink, try and get lucky with some xp awakens to make it even quicker.