The best is actually either a tauren pala/dk with the Sky Golem, as you move 20% quicker as either of these classes, loot herbs the quickest as tauren, and with a Sky Golem you are no longer dismounted when herbing.
However, with no sky golem it would be a tauren druid.
You can basically use any class just pick yourself up a pair of forager's gloves from Korda in Kun-lai and get yourself a sky golem - fast herbing, no dismount