The Avatar is a great amp. The new stock Mullards are very nice sounding tubes IMO compared to most. Do a google search and try to place the reviews of different tubes to your preferences.
Mullard EL34 that sounds best
Will need a matched quad of EL34 for the VAC Avatar SE integrated at some point. Currently using Svetlana SEDs but I guess Mullard should be better.
What particular Mullard would you recommend and why ?
I use Mullard 12AX7 longplates in preamp and RCA blackplates as driver tubes.