It should be noted that as they are bloodlusted fear should play only a inor role in this matchup. Poison could work but Ares could be immune due to Pre-Ascension Diana having it due to her immortality. The Witch King still leads 4 to 0 so far tho.
Going to go with the Witch King. Immunity to conventional weapon damage and weapon breaking just leaves him in a better position in most scenarios. That's on top of the fact the Witch King is a highly skilled fighter himself.
Fear Manipulation doesn't mean much due to Ares being bloodlusted. However, Ares might be a little harder to put down due his ability to boost his power through feeding on the Witch's King bloodlust.
As for Poison Manipulation, Ares MIGHT be resistant to as Wonder Woman is resistant to it but that doesn't equal immunity. The longer he's forced to engage with the Witch King, the higher the chance that the poison could start to affect him. Not to mention that Ares will be exposed to the poison everytime he strikes the Witch King.
Ares' other abilities, at least to me, will probably just stall the Witch King more than anything else.
I don't think this is a stomp. The Witch-King isn't capable of just putting Ares down in one go, WK just holds more advantages overall and they trump what Ares can throw at him. It would still be a fight, especially with Ares feeding of the bloodlust and conflict, it's just that it's in the WK favor.