I’ve just done some math to find out the most profitable decks to buy in terms of dust. Here are my results:
Demon Hunter - 1760
Druid - 1840
Hunter - 1920
Mage - 1900
Paladin - 1920
Priest - 1720
Rogue - 2000
Shaman - 1740
Warlock - 1960
Warrior - 1880
In short, Rogue is the best one.
I just have to emphasize that this might not be the best way to choose your deck! Remember you are free to choose the deck you want based on the cards too!
Hope I helped someone 