I will chime in too, since I have a 642 Neo also - but mouthpieces are very personal, so you'll have to choose what feels and works well with you.
I started out playing with a Yamaha 51D, and then tried the Dennis Wick/Steven Mead SM4UX - I actually like the way this mouthpiece plays, but my friends say they don't like the sound as much as the next mouthpieces I'll mention. It does "feel" like the center of the tone is "fuzzy" but I like the playability of the mouthpiece a lot.
I also play a Doug Elliot 104J8 and my wife thinks this one sound good. I think it plays very well too.
My current favorite mouthpiece is my Yamaha 53SH. It seems to sound really good on the 642 Neo, and it plays well also. Compared to the DE or the SM, it seems to have a brighter high range, but a little less room to move around in the bottom end (for me).
I really like all the mouthpieces I mentioned, but I guess I just pick what suits my mood at the time.
Good luck on finding "THE" mouthpiece! I hope it's a fun and musical journey!
My horn: Yamaha 642II Neo. My mouthpieces: Yamaha 51D, Yamaha 53SH, Denis Wick SM4X Ultra, Doug Elliot 104 J8