>Swordsman
>Wizard
>Archer
>Cleric
NONE OF THESE ARE DICKASS THIEF!
Archer can pick up Rogue, which does do backstabs, and can cloak. There's also the Scout, I think it was, that also has some sneaky stuff.
Swordsman will get Shinobi when Rank 7 classes are done. Already has Pirate. You can probably get a bit thief-y with both.
Personally I'm considering either focusing on 3x Wizard > 2x Sorcerer > 1x Necromancer for summoning Shenanigans, ooor, 3x Cryomancer > 3x Elementalist, because I LOVED the whole freeze things with ice magic, then deal massive bonus damage to them with thunder, synergy from RO. And from what I can tell, it's back in ToS at least for one of the Elementalist's skills.
Another consideration is 3x Hoplite > 2x Cataphract. Mounted spear knight is olev. And Hoplite gets to deal extra damamge to larger targets, while Cataphract does the same to smaller targets.