Diabloprogress base their statistics on the so called "normalized hero score", a figure extrapolated from the heroscore of the top 10K and how many of each class are in the top 1000 by paragon levels. Here's the outcome:
Barbarians and Wizards are the absolute dominators of softcore paragon leveling. With the buffs to Whirlwind and the improvement on Archon's Arcane Destruction rune, it was to be expected that such potent AoE farmers will top the charts.
At the very bottom sit the Witch Doctors and, somewhat surprisingly, Demon Hunters who are still in the possession of the bugged Trail of Cinders rune and its 1500% weapon damage over 3 seconds.

Hardcore paragon leveling, however, is a whole other story and here Witch Doctors shine the brightest. As hardcore farming requires nothing but a slow, steady pace, the revamped summons of the doctors are seemingly playing an important role in the inch-by-inch zone clearing. As old-time favorites for hardcore progress, Barbarians are once again making a top two appearance and are 200 points below the WDs.

Source: Diabloprogress.com