I prefer steel. Aluminum is too light and is easily scratched or damaged and with the punched hole will be sawed through like the pewter with the ball chain. Not familiar with zinc, and how it reacts to skin and weathering over time, but I'm not willing to find out in the long run. Personally, I think that steel is the best investment to go with as we all know pretty much how steel wears and reacts and the strength and weight of it is right. All the proper characteristics of what we saw on screen, the steel provides us for a replica.
But again, this is my take on the matter.
Canadian Issue ID "dog" tags are an aluminum alloy. They were stainless Steel at one time but have been aluminum from about the late 60's.
It's a moot point though when talking about the Wolverine tags.