Mullard EL34 that sounds best

Never heard of them. "Sound very good" is not good enough for me. Either I will stay with SED Winged, that are alright, or will want vintage Mullards.

I have settled in on the old stock Mullard EL34 XF2 with the single O getter.  The XF1 version,I have not heard, is too expensive and hard to find anyway.  The XF2 OO getter is the early version of the XF2’s and said to be the better of the two versions but to me and my system I really can’t hear a difference.  With patience and luck I was able to acquire 2 quads of lightly used new testing tubes for $80-100 per tube.  They have been the best sounding EL34’s that I have heard but they keep getting pricier.  Good luck!

Did you get matched or unmatched quads of used Mullard XF2 ? $100 for test new is not bad.

I have used a number of different brand EL34s, JJs, SED Winged and other current production as well as old stock Tele and Mullards.

In the end, I like Gold Lion KT77s purchased through Upscale Audio for their reliability and they sound very good.

@inna my Mullards were not matched Quads.  I was able to buy matched pairs to make one quad.  Another quad I purchased was sold from the demise of an amp.  They tested very close but one of the tubes was a Matsushita not Mullard.  (Matsushitas look very similar and were made at a factory in Japan using Mullard tooling.  They sound good not great to me).  I was able to find a single Mullard with the same codes and test values.  Took a little bit of buying and selling to get the quads together.
I agree the Gold Lion KT77 are excellent.  They are my favorite new stock EL 34 family tube.  They just don’t have the soul/tone that Mullards provide.  The Mullards just sound better to me on my system.