Of current production 12AX7 valves:
Ei ones seem to be the best sounding BUT, production is highly inconsistent so, you can get the best or the worst valve in your buy.
TAD 7025-S (Mullard style), seems to be more voiced like Telefunken ones (instead of Mullard) so, it works really nice in american voiced amps and, specially good in blackface types.
Tung Sol, is one of the best soundings, very 3D but, EQ is altered to boost bass and trebles. It's some kind of Mullard sound with the added gain of a chinesse valve.
JAN Philips 12AX7WA sounds good, but it's very sensitive to amp's EQ, sounds better with tone controls in mid position. Can go boomy with wrong EQ. (not new production but, easy to get)
Sovtek 12AX7-LPS, nice sounding valve but, very prone to microphony so, a bad election for combo amps.
Mullard re-issue, sounds good bad flat compared to Tung Sol (as NOS Mullards do). Better for hi-fi applications.
Svetlana 12AX7, smoother than EH, less gain than Tung Sol, well balanced.
JAN Philips 5751, probably the best souding one in simple designed amps, lower gain but whole tone.
Sovtek 5751, in Reverb Drivers or for Tweed like amps (12AY7 or 12AT7 substitute)
Tesla JJ/ECC83S, well balanced, not harmonically rich, durable. Some kind of flat valve that helps to better compare the changes of swapping other positions.
Electro Harmonix 12AX7, Well balanced, good in any position, the valve that works wether other valves don't do it, the valve that solves microphony issues. So, a good valve to have always in stock, as a last resource.
Sovtek 12AX7WA/WB, very poorly sounding, low gain, very reliable (usually stock in some new amps).
This all, more or less, is sums up the info I`ve got from reviews from The Tube Store.
TAD reviews could be biassed, since they re-label valves and they design some others.
Same with Harma, Groove Tubes or any other re-labeler.
The reviews of The Tube Store match my own experience with some of those valves.
And, as I said, there is no recipe for every disease so, you have to experience your self how do like the changes.