Best 12at7a, 12au7a?

NOS or Ei? Thanks. I would like to hear what are you using and where is best place for purchase? Thanks
Only you can make that decision. Get lots of tubes and try all of them. They are not that expensive and you can get them on say E Bay. I tried some Mullards in my preamp with very disappointing results. These same Mullards worked beautifully in my power amp. I find that Tesla work great in my preamp.
I hear RCA cl 12AU7A, to be best USA "valve", and word Telefunken diamond bottom, goes around as THE best 12AT7, for around $450 a piece!