The shadow(?) above the big one's belt creates a lot of banding because the line segments line up with the line segments that make up the belt outline. if it's meant to be shadow, perhaps make it a little larger? If it's meant to be anti-aliasing, then shorter segments would work. Either way, try to avoid having line segments line up like that, it creates "fat pixels" that make the art look blocky.
The hands and the foreground arm appear to be pillow-shaded. Don't shade around the outline, think about where the light would actually hit and where it wouldn't. On top of looking flat, pillow-shading tends to create banding too.