I used dynacorn and so did my buddy on his car. my friend is a body man by trade and he said the fit was as good as the gm panels he has put on. I know some people will disagree but I liked the way mine fit. dynacorn is the same people that is making the camaro body.
I have the Dynacorn panels on my 70 SS. They look as good as the originals. I'd be more concerned with who is installing them, than who's quarter panels you buy. Classic industries is a reseller who does not produce their own panels. Goodmark also makes a quality (quality from Taiwan?) panel.