Plastic shell with nickel jingles or brass…or maybe wooden shell with German silver?
Sometimes I bring 4 or 5 tambourines to a rehearsal so that I can fit the tone of the instrument to the texture of the music that I am playing and /or to give some variety. Different shell materials influence the sound as well as the makeup of the jingles. Brass jingles tend toward a darker sound and seem to give off more of the “Rock” sound while nickel jingles are brighter and might be a good choice to give some sparkle and drive to a ballad. I have even set up a tambourine with a combination of jingles and washers to get a tight “dry” sound. During a rehearsal, play along for a few measures with one tambourine and then switch to a different one. You will probably hear the sound of one of the instruments fit better into the overall texture of the surrounding music.
One of my tricks is to switch tambourines as a song modulates. Moving from a darker to a brighter sounding instrument gives the impression that the tambourine is changing key along with the band!