In spite of what may be a personal taste "collectibles" are
collectibles and should not have their marks and numbers painted if originally they were not, 
although some auction houses do it merely for an aesthetic point of view, so in my opinion is not a matter of what we prefer: painted or "au natural".
Anyway personally I love GLOCKs with painted numbers, but I prefer LUGERS, especially collectible ones, only with the GESICHERT painted, as they originally were.