Some of the art in here may be horrible, but I'm posting it anyway...
Don't compare, and if you are going to be critical do it respectively, like,
'I like it, but maybe you should make the eyes more realistic.' not 'This is horrible. The eyes are way too unrealistic, the hair is too long, and I think you should quit.' If you don't like it, just leave, don't comment about it.
Comment which one you think should be on the cover!