Conventional wisdom would have you believe that the reed is the most important tone-shaping component for a baritone or bass saxophone - but that's only half true. The reed is part of a team, and the other half of that team is the mouthpiece. Together, they share the role of creating your instrument's tonal foundation, and it takes both to create truly legendary sound quality. The good news as far as baritone and bass saxophone mouthpieces are concerned is that they don't need to be changed regularly like reeds do, so once you've picked out your new mouthpiece from this section, you can expect to get years of fantastic performance out of it.
Another half-truth of the woodwind community is the impact that mouthpiece material has on the instrument's sound. While there's no doubt that there is a difference, the interesting thing is that this probably owes more to the different shapes of the resonating chambers than it does to the materials themselves. Traditional mouthpieces - like the Selmer Paris S80 Series Baritone Saxophone Mouthpiece, Yamaha 5C Baritone Saxophone Mouthpiece and Rico Royal Graftonite Baritone Saxophone Mouthpiece - are made from hard rubber or a similar material, and while sound varies from one mouthpiece to another, they're generally known for their warmth and blending quality. Metal mouthpieces such as the Theo Wanne DURGA Baritone Saxophone Mouthpiece or the Otto Link Metal Baritone Saxophone Mouthpiece, on the other hand, are usually considered brighter and clearer, which is why they're so popular among jazz musicians.
Since even ebonite mouthpieces can sound bright and even metal mouthpieces can sound dark, the absolute best way to know whether a mouthpiece is the best fit for you is simply to listen to it play. If you're unsure which mouthpiece to choose, it might be a good idea to do a little research on your favorite players and see which one they use to get their great sound. And remember that ligatures and reeds matter too, so think about how all three parts will work together - when you take everything into consideration, you'll be much better prepared to pick out the perfect baritone or bass saxophone mouthpiece.