usually they say that silver paint lasts longer.
However, you should bear in mind that the rubber covering will wear off before the metal parts do. I saw it on my friends camera (he wore the rubber off a heavy use of less than a year) and it's looks quite ugly.
In addition, reading about the issues that people have with these cameras (including myself) - the camera will have other issues earlier than when the pait wear off.
I mean, it's not a Leica, and to my feeling, this camera wasn't desinged to last decades, so metal aging isn't what should concern you.
To my taste, the silver paint just looks better.