Can't find information anywhere on the contacts, are they silver?
In all likelihood, they're nickel. The thing that makes these jacks nicer than average is just build quality. One gets the impression when inserting the plug than the contacts' springiness won't weaken as much over time. But, the DIY community here has only known about them for a fairly short time, so we don't really know how well they'll hold up over the long term.
I had the impression silver and gold matched different usage patterns
Gold is a soft metal, so it really isn't the right thing for this sort of jack. If you were going to plug it in and leave it that way, you'd have a good argument that gold is better than silver or nickel, but that's not how people use phone style jacks. Gold's real advantage is one of perception: it's common to see phone jacks with a gold flash ring around the nose, but no gold on the contacts, which you can't see!
Silver is much tougher than gold. Not sure if it's tougher than nickel, but it is much more conductive than nickel. The main disadvantage is corrosion, but there's a lot of friction when inserting a phone plug, and silver oxides aren't very tough to cut through. (Not like aluminum oxide, for instance.)
Nickel is a good workaday material. Very low corrosion, decent conductivity, cheap. 99% of all jacks have nickel contacts.