Well, Ness has rosier cheeks, you can see his hair under his hat, he's taller, has a circular head, and is thinner. Ninten doesn't have red on his cheeks at all, he's got a wider face than a circle, you can't see his hair well from his hat, if at all, and he's explicitly less fit than Ness. While you may think they may be almost the same, there are several differences with look. That is Ness, there's no one else it would be. It's not Ninten. Have you seen the clay figures of the two?