COATED decal paper means that there already is a clear base to print on.
UNCOATED decal paper means that I would have to lay a clear base, dry, then print.
Any reason to go with one over the other? My preference it to go for QUALITY prints.... so if putting down an initial clear get me a better result than I will do that... but if it makes no difference they I will go with whatever is cheaper... as long as the quality is still there.
These decals will be used on engine components like valve covers and oil filters... so they need to be high quality and tough.