I have a pretty substantial NOS valve stash including all the goodies (Mullard, Brimar, Mazda, GE, Sylvania, RCA etc...) and there really is a massive difference in tone between the various NOS valves themselves, but they are ALL superior to any current production valve.
Thats not to say current production stuff is junk, you just need to know which are suitable for use in various applications to play to their strong points.
For example, I did a taste test on my homebrew AC30 (6V6s in the output stage though). The first preamp stage (V1) was won hands down by Brimar ECC83s. I tried a variety of preamp valves for V2 and V3 but the difference was negligable so I stuck with the Svetlana/Winged-C ECC83s.
A similar listening test on my H&K Cream Machine amp ended up with a Brimar ECC81 in V1 and a Brimar ECC82 in V2 (output stage).
I'm personally not a big fan of the JJ preamp valves, they're a bit dark and flat sounding (good for a bright amp though). I'd go with EH 12AX7s any day of the week from the current production options, they're a really tasty sounding valve.