Best 12AU7?

We can generalize about the sound of tubes, but you won't know for sure until you try them in your system.

The RCA Clear Tops are supposed to be good in the treble.  If you want to spend some crazy money, search for Telefunken G 73-R, a very specially selected 12AU7.  I've never heard them, probably never will.

I like Amperex 7316 but don't think they're airy, more of a midrange tube.

Call Brent Jessee and talk it over.  He'll have something for you.

I used the Brimar 13D5 several years ago and loved them.  In my SET, they were very clean and clear without being bright.  I had the RCA clear tops prior and the Brimars were in another league in my opinion with quite noticeably more detail.  Some have said they are a bit warm.  I did not hear that at all but I did not hear any leanness either.  Images were also more distinct.  They are just a great tube, if your sonic preferences reflect the qualities mentioned.  

I have a pair of Telefunken 802S Platinum Matched Pair Best 12AU7 for sale. Please reach out to me.

Telefunkin ,Siemens , all very good nos tubes from Germany 

I use 12au7 tubes in my DAC... have tried LaRadiotechnique, Brimar CV4003, RCA Clear Top, Telefunken amount others. These are my (4) favorites for sure but right now I have the La Radiotechniqe in and they seem play best with the particular speakers I'm using these days. These were never imported into the US so if you can grab a set, go for it. Not overly expensive either but really a spectacular presentation to to bottom. French tubes have a personality all their own. Just my opinion