I've always felt the Vandoren concept favored a warm, slightly diffuse sound that nevertheless held shape consistently throughout the various registers of the clarinet. For jazz playing in particular, I'm a fan of the B40 as an all-purpose "utility" mouthpiece.
This particular mouthpiece was chosen from a few, and plays very well in tune from the bottom of the horn to double C, produces a solid, warm tone, and can be used in a wide variety of settings, making it a pretty good mouthpiece to keep in the case as a backup. I've owned it for just about twenty years, and though it's never been my primary mouthpiece, I feel better having it around.
For those who like a full-bodied sound, but prefer a softer-edge than the cutting clarity of a Selmer C85, the B40 might actually turn out to be optimal. It doesn't articulate as cleanly as my Selmers, but the two seem complimentary mouthpieces in basic response--they take the same reeds and react almost identically, save for final tone quality.
There has been a big movement in the clarinet world over the past decade and a half, especially, towards very expensive custom mouthpieces. I have several in my collection, and have even recommended certain models to players--there are many good reasons to work with a custom mouthpiece designer. By the same token, there are horror stories of players breaking their one, perfect, custom mouthpiece and not being able to perform well without it. My personal philosophy is that a player ought to be able to play 'standard' equipment if needed. If your custom, deluxe, $700 mouthpiece shatters, you should be able to pull out a Vandoren or a Selmer and comfortably play a gig. This won't be everyone's attitude, but for me it makes sense--I wouldn't be comfortable if the only equipment I could reasonably handle had been altered to the point that it behaved like no other 'piece.
For that reason, I recommend that players know how to play on Vandorens and Selmers. As far as mouthpieces go, they are pretty consistent, intonation is solid, range is solid, and they are economical.
