Obviously Dio because he and Jonathan both played it at university. However, Kars is the ultimate life form, so, I would suppose he would have the perfect ability to play foot ball. He's physically stronger than Dio, and possesses every attribute he could ever need, on top of an intellect that would allow him to learn every rule to the game possible. The only thing I think he would have issues with are the penalties. I could see someone throwing a flag against Kars and Kars would just cut the ref in half over it, especially if he didn't do anything like is so commonly seen in football. Dio could probably control himself better in that regard. But if we're talking backyard football without any refs, then Kars all day long.