WoodSheddin wrote:Play the Sousaphone in the environment and under the conditions for which it was designed and mouthpiece choice becomes the silliest of considerations.
And the congregation said "Amen!"
The notion that playing outdoors (on any instrument) reveals the subtleties necessary to distinguish a good plastic mouthpiece from a good metal mouthpiece to my thinking begs for challenge. Those who curl their lips up at the word "plastic" because it blocks their art need to do some true comparing. That means sitting in the stands and listening (but not looking) to someone out on the field, in the middle of ensemble play, switch back and forth between plastic and metal and then being able to identify which is which. If you can't do this, then it doesn't matter. And you'll have to conduct the test fair and square before I'll believe that you can tell the difference. Noticing a difference (and not necessarily even which is better or worse) in a practice room or band hall doesn't count.
Choose the mouthpiece for comfort and durability. That's where Sean's boxer-shorts analogy is most perfect.
I have burned my lips on a mouthpiece that has sat in the Texas sun as often as freezing them on those remarkably cold Thanksgiving Day parades in downtown Houston. I have been required to make moves with my tuba that would make it remarkable that the mouthpiece would not come out, just considering the momentum and inertia involved. A mouthpiece in a sousaphone requires three friction-fit tapered connections. A failure is three times as likely as, say, losing the mouthpiece out of a concert tuba, even if they are subject to the same movements. And that has happened to me a couple of times over the years, too. Considering that marching instruments are subject to considerable motion dynamics, the probabilities are much higher. Yes, I have had my mouthpiece delivered to me after the band exited the field and someone noticed something shiny left behind.
And how many goosenecks have been mangled from people twisting those bits in that little bit tighter?
To answer Klaus's question, it's a matter of requirements. Using a sousaphone in a concert situation, i.e., sitting down on a stage, has the same requirements as for a concert tuba. Using a concert tuba in a marching situation has the same requirements as a sousaphone in its typical usage.
Using a sousaphone in a jazz band is a separate category. But even there it is often subject to significant movement.
Rick "noting that the Kelly line accommodates all the basic mouthpiece shapes" Denney
) that there's no such thing as "too much chocolate"! 
), nor would I take a "concert mouthpiece" out on the field if I had a workable alternative. Harsh conditions call for durable equipment.