El Pres, try contacting Reliable Arms. See if they still offer the finish options they had some years ago. IIRC, meron pa yata sila nung robar-type (NP3?) finish.
If not, chrome is the most durable. Black chrome, on the other hand, wears out like blueing if properly done
. Bad black chrome chips off like ordinary paint. Unfortunately, dito sa atin, I can no longer say sino yung pinaka-okay mag chrome. I suggest you go with somebody you already know you can trust para madali kausapin when something goes wrong.
Pinaka lowest maintenance ang chrome and will last long if properly applied. Blue looks gorgeous pero you'll need oil wipe downs everytime you touch it.