They both have stuns. At level 4,
Wraith King's stun is 2 seconds. Chaos's stun is 2-4 seconds. So, no matter what, it won't be any less of a stun. Edge:
Chaos Knight
They both have a passive big hit ability.
Wraith King's is 15% crit with extra crit damage.
Chaos Knight's is 10% with extra crit damage. At level 4, both have an extra 300%. Edge:
Wraith King