I would always check MB first. In my experience the panels fit better, feel better and look better. However, not all panes are available from MB and they are definitely more expensive.
For aftermarket sheet metal, I like SLS out of Germany. Very fast shipping, no taxes and the quality is good.
There is also K&K out of Sparta, MI, which a lot of members seem to like.
Personally, I had no luck with the polish vendor listed in the tech manual.
Hope that helps to get you started.
Dirk