I like the EL34 a lot. The JJ is good. I got an NOS tesla and and it’s a little less powerful, but these tubes saturate like crazy. I haven’t spent a lot of time with the KT66 yet, but it sounded pretty good. EL34 is my fav right now.
As an aside, one thing that makes this amp great is it has allowed me to swap out more parts of the signal chain to experiment with tone. I’ll try guitars with different pickups with my other amps and that makes some difference, but to be able to swap power tubes has really been a lot of fun to mix and match and see what it does to the tone.