My personal horn is the Yamaha 667. The last time I had the opportunity to purchase horns for the school, I went with the 567. Of course part of that decision was that it is the step down from the 667, and is also a Guyer wrap. What really sealed the deal was when my HS horn player played on it, her sound opened up and the horn fit in her hand better than the Holton she was playing on. I would also look at the Conn 6D, especially for MS players....a very forgiving instrument for a younger player. I am not familiar with the 671, so I can not comment on them.