Depends on your problems- are they intonation problems? Is the low end sharp and the high end flat? If so, get something a bit shorter in length and larger in chamber and that should help.
If I didn't guess right, let us know what the specific problems you are having with the mouthpiece (or maybe horn...) are and maybe we can help.
If I didn't guess right, let us know what the specific problems you are having with the mouthpiece (or maybe horn...) are and maybe we can help.