I've used German (nickel) silver quite a lot. It's available in different tempers; if you purchase it from an electrical supply outlet it will be dead soft 99.9% of the time. You can purchase it from TRL however in half hard temper at a reasonable price.
However, nickel silver is known as the "allergy metal", since a high number of people have a skin allergy to the metal. It is also darn near impossible to cut anything over 20g using a JumpRinger or other coil cutting device because it burns your blades out faster than copper or brass. A cheaper alternative to silver for teaching beginners or just to use to learn on is bright aluminum. It's about $5.00 a pound for the wire, and anywhere from $18.00-$85.00 (depending on gauge and ring size) for a pound of machine cut rings. You get A LOT of rings in a pound; for say 18 gauge 3/16" ID you get in the neighborhood of 4,500 rings. If you're not making your own rings but don't need that many, you can purchase them by the ounce as well, using the same gauge and size listed above you get a little over 550 rings per ounce. I find it preferable to use aluminum to teach students with for a few reasons; almost no-one is allergic to aluminum, it's cheap so no need to worry when a student mars rings or sends them flying across the room as they are easily replaced, the temper is hard enough that it is easy to teach someone how to close rings correctly, and I can offer classes at a significantly cheaper rate than people who teach using sterling or gold as my over head is much lower.