Overall, story > art.
there is a certain minimum standard required, but really it depends on your target audience. age? tastes? how good at art are they?
if your art isn't all that, your story better be. but so long as the story's good, the art will improve with time anyway, and people will be interested. there are some really successful comics with art that's often quite ugly, and while some of them may sell on name alone (long standing franchises that is,) others, like Runaways, had 'bad' art from the beginning but was massively popular in its time. (also, funnily enough, the original Runaways artist makes amazing artwork these days)