Originally Posted by Raymond62
There are more clarinets to choose from than just those four, too (e.g., the Ab sopranino above the Eb soprano (which is above the Bb soprano), and the Eb contra-alto and Bb contrabass clarinets, below the bass clarinet).
My first real instrument was the clarinet, and I've played in a number of quartets over the years. The most common arrangements are: 3 Bb sopranos + 1 bass, or 4 Bb sopranos. Second most common are: Eb soprano + 2 Bb sopranos + bass, or 2 Bb sopranos + Eb alto + bass. Everything else is much less common (although I've played a quintet scored for Eb soprano, 2 Bb sopranos, Bb bass and Bb contrabass).
Modern arrangers often write an alto part only where the range demands it, and then often provide an alternate 3rd part for Bb soprano or for a second Bb bass.
If you limit the arrangement to Bb sopranos and basses, just about any elementary or junior high school band will be able to cover the parts. If you include an Eb soprano (or A soprano, Eb alto, Eb contra-alto, or Bb contrabass), only high school students (and higher) will be able to cover it. If you include basset horn, Ab sopranino, or soprano in D or C, very few will be able to play it (or most will play it on other clarinets, transposed) - typically only professionals have these horns.
There's nothing wrong with using an Eb soprano for your top line, if you have good players. They do have a distinctly different timbre from Bb sopranos in the low register (although it may be that only clarinet players notice this), and can be difficult to play in tune in the very high register, but experienced players can be counted on to play in tune. If you want subtly different timbres in the melody, alternating between Eb and Bb sopranos is one way to go.