Okay..... So! Buu-han is actually NOT the strongest form of Buu mainly because he is not a form to begin with. He is a variant of super Buu, because buu-han is a fan made name, the actual name is super Buu (WITH piccolo, Gotenks and gohan absorbed) but still in his super Buu form. So it's mainly super Buu (normal) vs kid Buu (since this is his normal form) and for it to be more accurate it'll actually be "buu-han" vs "kid buu-han" so basically it'll look like this....
Super Buu (with piccolo, Gotenks and gohan absorbed) vs kid Buu (with piccolo, Gotenks and gohan absorbed). So since this is more accurate who is the winner?