The NOS ECC83 Mullards, which made before 1970's, during 50's are the best, imo. They are not dull or to warm or what ever, they are just great. I rolled lots of ECC82, ECC83 in my previous Primaluna Prologue Two and ended up with NOS GEC KT88 + ECC83 Mullards + CV4003 Mullards. Even in my CDP still sit 2x ECC82 Mullards. I also highly recommend NOS E83CC TESLA or ECC803S at least, but dont mix up them with general ECC83 or fakes, cos they are nothing alike, here you can read all info you need http://www.jacmusic.com/nos/ECC83-part-numbering1.html
Further, I tried all kinds of TUNG SOLS, TELES, BRIMARS, TUNGSRAMS, PHILIPS, SYLVANIAS, but still prefer truly NOS Mullards. You can make some nice combination, where not only the Mullards are in, but say TUNGS SOLS BLACK GLASS + Mullards, but better would be BRIMARS and MULLARDS, but than again, made during 50's or earlier 60's
One last, but sure not least, is Mullard CV491=ECC82, but than again, sorry for mentioning this over and over again, but you need the one from 50's, this one
http://www.tubedepot.com/nos-12au7-mullard50s.html
I know that it may sound bit to Mullard, but thats my conclusion that I have based on years of tubes rolling, where folks see them as warm only, which is not the whole true, imo.
About EL34. I only tried NOS TESLA's and found them a very good alternative to NOS GEC KT88.
Good luck and hoping your wallet can handle it:)