I find Kyle to be annoying at times (A tier is still great). Stan, I find to be more relatable and likeable and see him (as well as Butters) as the heart of the show. I enjoy his more down to earth personality more so than Kyle's idealistic personality
I can understand Stan and Kyle going up to a B, but not an A nor S, they are not that incredible in my opinion. The others, I agree and disagree with most on what they are ranked.