Stainless steel chain is my new favorite chain!  It is a little darker and more gray than sterling silver, but I find most people end up wearing their sterling chains slightly oxidized, in any case.  If you keep your sterling chains clean and shiny because you like that look and feel it's worth the trouble, then spend a few extra dollars on sterling silver.  If you don't, save some money and go with the strength and durability of stainless steel.