undertale one is shocking. it's chaotic and the visuals are disturbing and it's overall an incredibly dramatic fight
the uty one is a lot more visceral. the visuals are chaotic yes, but it's the implications that are the most disturbing. the visualization of flowey's suicidal ideation and the fact that instead of it being "you're the only thing standing in my way from being a god" he's literally just torturing Clover for the hell of it really makes the fight
i like both of them pretty much equally tbh