Best 12AU7 Type Tubes for a Preamp

The prices you list for two of the three nos tubes is excessive.

The RCA cleartops shouldn’t be $40 each.

The Mullards go for around $175 a pair, unless they are the m8136 variant. Then they’re around $250 a pair.

If you can find a strong tested pair of the Amperex 7316’s (the earlier the better) for $150 each, I’d get those in a heartbeat. 

I've already expressed my preference for NOS tubes and to buy from a reputable dealer, but I must give props to Psvane. My preamp came with a Psvane 12AU7-S with gold pins and it had very nice tonal qualities. It presented a wide soundstage, but lacked the depth that so many NOS have. Nice top-end, not etched like some of the Russians, just a pleasant sounding tube that works very well when combined with NOS.

the PSVANE ART-S series are pretty tough to beat sonically.

If you are looking for more midrange warmth, the RCA black plates are a great choice. 

Brimar CV4003 from Upscale worked great in my Rogue RP-1 and RP-5.
The RCA were brighter.
Genalex Gold Lion we’re pretty good as well. 

In my Backert Labs Rhythm 1.3 I use NOS 12SN7’s with the proper adapters in place of 12AU7’s and the results are wonderful.