The answer is always “the one that works best for your needs”. Ok, that’s me being Captain Obvious but in all seriousness it sometimes is that easy. Other times you might have to think a bit about what you are after.
I can’t tell you how many times I have been asked “what’s the difference between NY & Deco shapes? Is it only cosmetic?”. Now with the Nouveau blank it could get more difficult to choose… or is it. The shapes (Blank is what I call outer shape) are unique, but it’s not just the shape that is different, it is the weight of the mouthpiece. The weight of the mouthpiece really does control many things in the sound and feel of the instrument.
A heavier blank (Deco) will provide a very stable feel and if your instrument is not very stable feeling this is the mouthpiece for you. The sound is also very rich and centered aiding in projection. This all sounds perfect, why would you want anything else but “rich and centered”? Well if your horn is a very centered and stable instrument then this style mouthpiece might double up with your instrument and make the overall sound confined and not allow you to shape the notes the way you want in timbre and color.
The NY blank is my medium or standard weight mouthpiece. It has a very neutral approach and is not heavy or light. The sound is wider than the Deco with a bit more highs on the outside of the sound than the Deco, and this style of mouthpiece is a safe bet if you read all of this information and still can’t make a decision.
The Nouveau blank is a very light mouthpiece that is designed to open up instruments that blow a bit tighter and are overly centered. The sound is the most wide and brilliant of the three styles of mouthpieces.
The one thing to realize is your style of air. If you blow very slow hot air and tend to be really dark sounding without enough clarity then you should consider a smaller mouthpiece in a lighter style blank to focus in your sound and help with clarity within sound and articulation.
If you play with very fast air and tend towards being bright and a bit explosive then consider a heavier style blank to keep the sound centered in the higher dynamics and the upper overtones from being too prevalent in the sound.
Everything is about balance and understanding what you want in feel and sound. There are enough options within this line to fit most any trombone player. If not, then just wait for the Alessi line and then you will have even more options to think about.