This is the most thorough answer I managed to find so far. They do mention silver being more valuable, but seems like the application process might be more expensive also.

The only source I could find on commonality is this paywalled market report claiming “The market is segmented by application (home and commercial) and type (aluminized and silvered glass mirrors), with silvered glass mirrors currently holding a larger market share due to their superior reflectivity and clarity.” Not sure whether greater market share necessarily means more individual mirrors produced though. But sounds like silver still reigns supreme despite higher costs, though not sure by how much.