12au7 tube question?

Is there a substitute for the 12au7 tube, like there is for the 12ax7, that has better sonics and microphonics? Of the many brands available, which are considered the most transparent, and pure sounding, compared to colored or lush, one note bass, etc.

The European equiv.s are ECC82, ECC802s, CV4003. Go to Joe's Tube Lore at AudioAsylum for a detailed evaluation of 12AU7s. In my system, I liked Amperex Holland Heerlen labelled Dumonts best.
Swampwalker's advice to review the info on AA at Joe's Tube Lore is good. I have found his information to be helpful to me. I am following his advice and am awaiting delivery of Amperex Holland Bugle Boys which he favors.
Specific to your search for info on 12AU7's, while you are on AA, search for postings on 12AU7's by Robert H. Several on AA seem to hold him in high regard as the resident 12AU7 guru.
What are you currently using for 12AU7's? My favorites in descending order are:
1) Telefunken
2) Amperex Bugle Boys
3) Mullard (please note that the CV4003's in the white boxes and sometimes called 'mil-spec' ARE NOT NOS, but modern crap manufactured in the '80's, and usually sold for obscene profits. No Mullard label on these dogs!)
4) RCA 6189's

The Telefunkens have it all...deep clean bass..airy and extended highs, and an incredible presentation of soundstage. Be careful, as there are many fakes out there. Be prepared to spend $200- and up, for a genuine NOS matched pair from a reliable source, if and when you are able to find them!
Yes. Lots of choices. However, as others have pointed out, a MIL or industrial number alone, does not guarantee that what you are buying is better. If it was made during the peak of vacuum tube production it will be better than towards the end of production. There were some common tube types, manufactured in the millions, that perform just as well as their more exotic MIL or industrial counterparts. I would contact Antique Electronic Supply and try some RCA 5814 or 5814A if they have them, especially if those tubes date from the 50's into the 60's. Not 70's. Other main stream NOS brands of this vintage would probably be worth a try. The 5814 draws slightly more heater current, but it should not be a problem.

There are other versions that were made to withstand various vibration levels, shock, voltage swings on the heater, and so forth that may not have anything at all to do with sonic performance. Some of these carry fancy numbers and fancy prices. NOS 12AU7's that are mainstream brands would be worth trying. Any tube produced in quantity probably achieved a fairly consistent performance level and stable quality in production.