I had a brass Copeland in D, and I've played someone else's nickel. The brass sounds warmer and richer than the nickel, but the nickel's brighter and louder. Brass tarnishes like a sumbich - I don't think the nickel's as bad. I don't believe I've played a silver one.

If I could play, and I could afford another Copeland...well, D's best for playing with others, but I LOVE the way Bb whistles sound. Possibly nickel this time.