What are good metals for trombone bells?

[ParakeetofMusic]

I am a freshman at high school and am curious about different metals for trombone bells. I am currently plaing on a Buescher with a yellow brass bell for jazz and a rose-brass Yamaha closed wrap for concert. I have heard about different options for the metal on your bell and I would like to find out if the metal makes a difference, and if some metals are better than others.

Any help is great,thanks!!