I own all of the tubes being discussed, as well as the Siemens / Telefunken AEG. The Teslas I recently bought are the blue glass version, a nice alternative to the clear (same performance). I would rate all that I own in the following order, from most to least favorite:
Mullard dual getter, welded plate EL34. Mullard single getter, welded plate EL34. Amperex double getter, welded plate EL34. Amperex single getter, welded plate EL34. Same brands as two previous, without welded plates. Siemens /or Telefunken AEG EL34. Tesla E34L (all colors of glass). Electro Harmonix EL34. Sovtek EL34. Svetlana EL34. Chinese EL34.
This list does not take into consideration old EL34 tubes that may have been constructed around the same time as the vintage Mullard and Amperex. It may safely be stated that the older the tube is, the better the quality and sound, provided they are not completely worn out.
I recently purchased some old EL34 tubes marked Dynaco. These were manufactured by Mullard for the Dynaco Stereo 70 amps of the early 1960's. The silver was almost completely gone from the inside, and the base had been scraped with a knife to remove a previously applied sticker. The plate showed signs of having gotten too hot (scorch marks), and most of the logos are missing. After all this time and abuse, it still out performs every current production tube I own.