ill vote for IK helm
reason:
-get the 3rd set bonus which is dmg reduction from melee. stackin that 3rd bonus with the stat from ur helm gives a good def towards melee mob.

and also i think that melee reduction dmg ignores mob lvl unlike all resist, the higher the mob lvl, the less effective the resist is. correct me if im wrong.

-i bet IK helm has some core stat which might be a plus compare to mempo.
-crit chance ftw

no doubt IAS, AR is a good stats, but personally, i prefer the CC and the melee reduction.

omg your chest armour...

get something with 400+ stats