Round 1: Stomp for Kars. Pillar Men > Vampires which are just lesser versions of them made through human physiology altered by a Stone Mask
Round 2: Hard to say, Kars can’t be put down by DIO as the Ultimate Life Form where he’s now completely immortal but has nothing to counter DIO just pounding him endlessly through time stop spam.
I say DIO after beating Kars into submission, especially if it’s DIO after he’s consumed Johnathan’s blood