I've never tried the standard Mullard ECC82 unfortunately. But, the M8136 version which was an upgraded version for long life, precision use for the military does sound the most articulate out of the 12au7 tubes I have.
I'd say it's on the warmer side of neutral but certainly not overly so, detailed with great bass extension. Cradle to the Grave on the Hostiles movie soundtrack, you really feel the bass rumble... seems to go very deep. It's not a flabby bass either, tight and impactful with a certain force to it. That said, when new and burning in the bass is a little loose but not for long. It's one of the few tubes that I really enjoyed straight off from new. It has some great bass punch when listening to EDM as well.
Mids have a nice sweetness to them, very clear and the highs are well presented but not overly extended or rolled. As you said, it's just more articulate and detailed than most other tubes I've listened to. As well as the mids, layering, imaging and soundstage depth are my other favourite aspects of this tube. Instruments and voices are layered so you can clearly tell where they are but it never feels like a collection of individual elements.
If you do go for one, try and buy the ones with the old shield logo rather than the new one. The new logo is used on tubes from 1970 onwards and I've noticed they have a little more edge, grain to them... especially in the highs. I don't think there is a big difference in price, just takes a little more looking around as the new logo versions are more common.