What do you recommend?
I don't DPS on my Sin, nor do I have any real desire to, but from what I've heard, the "Mad Maul" spec is good. There's a guide for it somewhere on the 1st page of the Assassin forums. As far as Sorc goes, Lightning does higher theoretical DPS, but is not very mobile. 31pt Madness is pretty close on a dummy and suffers a lot less from moving around.