If you're playing with the Trials on -- Barrier and Guard get you rekt, or sitting there rubbing your face with boredom as you wait for your party who's perma-controlled the guy to chew through his 35,000 point Guard, or a Barrier that's resisting the main magical damage you packed in your little kit.
A good geared rogue with right passive can keep armored shredded on multiple targets all by themselves, no reason to pack it on a weapon. Get attack, or Guard Bonus, Sunder and Armor Pen are worthless if you built your characters right and decked them out.
Leather Offense, while we're on the topic:
Critical Chance -- you can't 100% legitimately, so take it, there's too many effects that proc from it. Flanking is wonky, and really, unless you grabbed a Deepstalker Sigil, I wouldn't worry about it. Critical Damage is useful if you can get over 30% critical chance, and of course Sunder on Hit is useless with Critical chance.
Cloth:
Attack or Barrier damage -- depends entirely on much Dispel/Purge you're carrying in your party.