Also, art is quite personal. Your favourites are different from mine, even when the same artist is involved. Another thing is originality. A longtime favourite of mine, Rembrandt's The man with the golden helmet, is now considered to be mainly the work of one of his pupils. You are pretty safe with Magritte and the Maya, but there are more paintings considered "school of Breughel" than "Breughel" now. Next, artists are unevenly divided. You can't pick one for each country. Who is the best-known Luxembourg artist? Who could represent Denmark on Goya's level?
Having said that, there should be a place for famous art works in metal. No full replicas, but some significant detail on large brushed steel medals, maybe?