Not so often mentioned when comparing frame materials is scratch resistance.

It seems as if carbon fiber frames would scratch most easily, followed by....

Softer aluminum alloys may be next?

Titanium is thought by many people to be hard and scratch resistant; but that may be more a function of the word titanium, and its popular images and associations, than of facts. I've talked with people who are surprised by how easily their ti frames have gotten scratched [though I also wonder whether titanium scratches (the smaller ones at least) can be rubbed out].

Does anyone know if there are numbers out there?

It seems as though 853 and 953 might be among the more scratch resistant materials, but I've never seen numbers.