A student who is encountering the clarinet for the first time should choose a Bb clarinet made of ABS plastic. Such an instrument is less sensitive to minor bumps and moisture inside and is also not as expensive.
Those who have already gained some experience and playing practice with a clarinet can answer many questions themselves. You should choose an instrument made of grenadilla wood. Bb or A clarinets are the most versatile. Whether you choose a clarinet with a German or Boehm system depends on your playing experience and the music style you are comfortable with. Both systems have their advantages and disadvantages. However, a skilled clarinet player can compensate for the peculiarities of each instrument accordingly.
Professional musicians often have both an A and a Bb clarinet and switch between them depending on the musical piece. Depending on the chosen musical style, a clarinet in soprano or alto tuning expands the repertoire. Many clarinetists experiment with different mouthpieces (shapes and materials), reeds, and ligatures.