Good question. Conn 4M sopranos are very hard to come by these days. There were very few of them made. The New Wonder Series II straight soprano saxophones were a great horn in their day, and seemed to have better intonation than the earlier Series I curved sopranos and the later curved 4M soprano saxophones. Soprano saxophones are much harder to play in tune than either an alto or a tenor, and while tenor and alto saxophones have more room for error, intonation is even more critical with soprano saxophones. I have both a New Wonder Series I curved soprano and a New Wonder Series II straight soprano, but the only soprano sax that I play professionally is a Keilwerth SX-90. The reason being that the Keilwerth plays so much easier, has much better intonation and a better sound overall. Conn 6M, 10M and 12M horns are wonderful horns with very good intonation and amazing tone, but I would buy a more modern soprano.

But would you totally discommend buying a vintage Curved Soprano? Or just the 4M...and what about the other American soprano saxes(like Buescher, Martin, king).

I would recommend a straight soprano over a curved soprano; new or vintage. They generally have better intonation and they're easier to play. The 4M is not a bad horn. For a vintage curved soprano, they are about as good as you're going to find. But, like any vintage horn (especially sopranos), they can be fussy and tempermental. If you want a curved soprano with superb tone and intonation, consider a new Yanagisawa. You'll have a lot easier time with a new soprano vs. vintage. Jim