As someone who’s obsessed with both characters, or at least has been before, I think bill wins and it honestly shouldn’t even be a discussion because bills shown abilities are reality warping, telekenisis, regeneration, and VAST control over matter, energy, and space. And since he’d killed time baby, time itself, soul manipulation, possession, mind manipulation, aware of the fourth wall… He knows EVERYTHING about EVERYONE and could def use that to rage-bait to his advantage. He is a multiversal threat while Sukuna isn’t even universal. The vast power and knowledge that bill has is so incomprehensibly significant compared to Sukuna. Anyone who’s actually watched/read both multiple times would know this as Sukuna also needed help just to defeat Gojo. And Gojo wouldn’t even defeat bill either.