Which tank?

[Absurdity]

It heavily depends on what kind of content you do. In general gameplay I would say PLD, WAR and DRK all have rather simple rotations, PLD only becomes complex once you get into otimization. The same goes for GNB, except that it starts off a bit more complex. DRK and WAR stay about the same, optimizing oGCDs on DRK isn't really more complex than Gauge, IC and Nascent Flash usage on WAR