With how the games actions are currently set up I think the Thief Rogue is definitely one of the most useful classes (not that I've done any research mind you). Two bonus actions per turn is great, pop a haste potion and get the two ordinactions and you suddenly can make two sneak attacks per turn if you want to (one ranged and one melee).
Sure, it's cheap and probably unintentional. But I will admit to abusing the system and having Astarion carry me through the Gith Fight in my most recent play through.
