Clockwise from left - A, Bb & Eb clarinets
Clarinets come in a variety of sizes from the tiny Ab sopranino (though this is rare) down to the Bb contra bass. The most common of these is the Bb clarinet, sometimes referred to as the soprano clarinet. If you're just starting out, the chances are this is the clarinet you will start on.
If you are very young, or very small however, you may find that you find the Bb clarinet too big a stretch on your fingers, or too heavy. If this is the case you should consider starting on a smaller Eb (Kinder) clarinet, or a Lyons C clarinet. These are smaller, lighter, and have a more simplified fingering system to the Bb model. Your clarinet teacher will be able to advise on the most suitable option for you.
Wood or Plastic?
Beginner clarinets are usually made from plastic (ebonite/resin), and have nickel plated keys. While they don't have the same tone quality or projection, they are more robust and easier to care for than those made of wood.
There are varying qualities of plastic clarinets, ranging from £75 - £400 for a new model. You should aim to buy a clarinet from one of the reputable instrument makers, Selmer, Yamaha, Buffet, Boosey & Hawkes etc. They build their beginner plastic clarinets to the same standard as their professional wooden models.
There are a few cheaper 'budget' plastic models out there, Lindo, Sonata, Artemis etc are popular examples. While these are perfectly nice playable instruments I don't think they possess the same tone quality as those from the more reputable manufacturers. They also don't seem to be as robust. In many cases, once outside the 12 month warranty period, it would more than likely be cheaper to buy a new one, than to have the old instrument serviced or repaired.
While there are some plastic clarinets for sale, described as being 'professional models', wooden clarinets are the choice for intermediate and professional players. They offer a far superior tone quality and playing experience. They are however more expensive and difficult to care for. A wooden clarinet is more likely to crack if put away wet, dropped or exposed to extreme temperatures. The key work on wooden clarinets also tends to be silver plate, and more slender in design. This makes them easier to bend if mishandled. If you are a beginner or inexperienced player, these instruments are best avoided.