Best 12AU7?

If you are using this in the buffer stage you recently posted about I would not drop a lot of coin into tube rolling.

Maybe try an RCA clear top as they are clean sounding and cheap as chips to see if it makes much of a difference.

I use expensive vintage tubes in my inexpensive kit gear, but in gain and driver stages.

DeKay

Agree Telefunken are the best I have heard for a detailed brighter sound.  Rca cleartops are an amazing value and sound extremely good on the brighter side as well. Can’t go wrong with either.

I really like the mil spec triple mica black plate RCA 5814A I just found. Detailed, smooth, not dull, and not too bright either.

Upscale Audio has very good NOS and new tubes. Check them out. 

Also, Vintage Tube Services - Andy Bouwman.