I've been using JJ's since they've been known....I think. They're cheap, last a long time, and sound great. I don't know what else you could want.
And here's some truth......Myles Rose....GT tube guru and associated with 65 Amps.....he's forgotten more than most people know about tubes. He says the JJ EL-84 is the one to buy, for current production tubes.
And I don't need anyone to tell me about their E-34L's. They're cheap and happen to sound great.
I'm not discounting any other tube brands that are excellent, but for power tubes JJ are the best overall value.