I agree with Beekeeper on the second part of his post, not really on the first part. Between my Challenger and Cuda I have used a wide variety of sheet metal from a variety of vendors. I will say without reservation that AMD is superior to the others by a significant margin. It comes down to 2 main issues, fit and metal quality. I have found that while most of the panels will fit to one degree or the other AMD's overall quality (metal thickness, correctness in the stamping, and dimensions) are typically far better.
All this said, I might use someone other than AMD for something that won't be visible or isn't overly structural, but when possible I would definitely use AMD for things such as fenders and quarter panels. The floor is a judgement call because while it is structural (obviously) it is supported 360 degrees as well as via cross members. If you plan to use some sound deadener such as Hushmat it might be a wash as the deadener will add to the rigidity.