The One Ring of Trombones
In many ways, most common brass instruments could be pared down to one model of instrument and no harm would be done. For example, if the only kind of trumpet in the world was a Bach 37, very little would change. Orchestral players would have to get used to not using C trumpets and/or rotaries, and high baroque and solo repertoire would be more difficult. But overall, business would pretty much continue as usual. The Bach 37 is played by many players in every style where a trumpet exists, and it works perfectly well in all of them. I personally have never played a Bach 37 I’ve liked, but it would still be my immediate suggestion for the only model of trumpet in the world.
Horns are even more flexible; you could pick an Alexander 103 or a Yamaha YHR-671D or any number of other popular double horns as the world’s only kind of horn and no harm would be done (apart from in historically-informed performance, but that’s a casualty in any of these “one instrument” scenarios).
A Besson Sovereign would be my pick for the only euphonium, but it could just as easily be a Yamaha YEP-642. Tuba is a little more difficult, but you can just pick one that’s pretty good at everything. For my money that would be a British compensating E-flat, such as a 19” bell Besson.
Trombones seem to be the most difficult; you need to find a trombone that can do everything, from alto to contrabass. That means screaming 4-hour salsa gigs, stratospheric Bill Watrous or Dave Steinmeyer jazz ballads, delicate Mozart alto trombone parts, heavy Mahler or Wagner orchestral parts from 1st to 4th, wild Broadway pit books, earth-shaking low blasts in modern film scores, and more. You don’t get to have one alto trombone, one small tenor trombone, one bass trombone, and so on. You can only have one kind of trombone, total.
Of course, there is no answer to this question that doesn’t compromise in some way. No single trombone can play alto and contrabass parts equally well. We need to find a trombone that can do everything decently enough that trombone players would be able to make it work. To me, that means it needs to be a medium-sized tenor trombone with F attachment that isn’t picky about what mouthpieces work in it, has an unusually beefy low register, an easy high register, the volume to project over a salsa or rock band, and a very “vanilla” trombone sound that is easily colored.
What trombone does all of that? Easy: the King 3BF.
For my money, the 3BF (along with its slightly larger stablemates, the King 3B+F and King 607) is the most versatile trombone of all time. I have used mine to play every tenor chair in a big band, lots of salsa gigs, New Orleans jazz, bebop combo work, principal trombone in an orchestra, brass quintet, Broadway books that go well into the bass trombone register, entire classical trombone sections top to bottom in recording sessions, and more. No, it doesn’t have as beefy of a low register as a bass trombone, but you’d be surprised at how much sound you can put through those low notes on the 3BF. The F valve has an E pull as well, so even if we don’t get to have 2-valve 3BFs in this hypothetical one-trombone world, we’d still do just fine on the low stuff.
Now the 3BF is certainly a bit biased towards the brighter, higher commercial side of the trombone’s oeuvre. The 607, being just a bit larger but otherwise the same, sits more right down the middle between the orchestral and commercial sides of the spectrum. The very high register (D5 and above) is just a bit more work than the 3BF, but in exchange you get an absurdly beefy low register (better than most large bore tenors in my opinion!), and a sound that more easily fits into the darker classical mold while still easily being able to play as bright and punchy as you need for any other genre you might find yourself playing in. But the 3BF and 607 play very similarly, with only a small difference that is mostly noticed when playing them back to back. On their own, you pick either up and it just works immediately, in any style. As an additional plus, these trombones are very easy to play and can handle lots of abuse, so it wouldn’t be a bad situation for beginners either.
It’s an easy conclusion for me. If the only kind of trombone in the world was the King 3BF (or 607), we would be just fine.