Most Musical 6NS7 tube for a Preamp?

One more vote here for the Don Sachs preamp. You won't regret it musically, and it is perfectly in your price range. Also very easy access for rolling tubes.

I would look for a Rogue Audio Magnum 99 pre and then you can roll all the 6SN7's you like. I tried them all and some of the variants are just better. I went from the 6SN7 to the 6F8G's and then to the 6J5GT's which will require and adapter, these are by far the most linear of all....

The word musical means different things to different people. It’s just word. There is a very large audiophile vocabulary for sound which oft goes unused. Anyway, you can’t go wrong with Sylvania NOS of almost any type, Chrome Domes all the way up to ‘52 Badboys. Then, more progress can be yours for the cost of Herbies tube dampers. They’re gold, Jerry, gold! All tubes are microphonic, even ones that claim ultra low microphonic. And two dampers are better than one, one of the glass at the level of the getter the other on the base. 🤗 Yes, I know what you’re thinking, “but don’t two dampers cost more than the tube itself?”

@ozzy62. Your assessment of the deHavilland is correct that why it requires the changes I mentioned above. Just adding audio note resistors will change all that around $60 for the two non-magnetic or over $100 for the silver versions.  Add some nicicons and v-caps and almost there. Change out that junk of a transformer and you are there.   Of all the 6sn7 tubes the CBS 6sn7 sounded the best for $15.   Happy listening

In the past I wouldn't give you a nickel for any Chinese tube but the recent new Dawning Series tubes out of Shuguang are excellent.  I recently bought a Don Sachs all in preamp and he suggested them and they are lush sounding.  WE6SN7 PLUS.