To be fair, I'd take either or. Both are great in their own ways. If Absolute Will is taken as Omnipotent Will, then I honestly don't know which one I'd choose!
Omniarch grants you lordship over everything. Thus you'd be above it in concept. Stay with me now, considering Omniarch users rule over everything then in technicality they're superior than the said thing they rule over. Therefore ruling over the concept of willpower could theoretically grant you an absolute willpower.
@Mr.Interest I follow your logic. With Omniarch, you'd have your own Absolute Will with the added benefit of being unaffected by any others who may have this as well. A lot of people can have infinite willpower, but only one can rule Totality!
@Godking25 It's whichever version of Absolute Will you want it to be. I understand, though. Omniarch is inherently Omnipotent while Absolute Will is not.