Yes I like EL12 a lot, even though it is not a fit for this amp strictly looking at the datasheet. But it sounds great and I have not had any trouble with it yet. My other big favorite is GEC TT21 which is similar to KT88. But I had trouble with a pair of TT21 after a while. GEC KT66 is very nice too. I don’t like EL34 sound, 6L6 sounds better to my ear. Never tried TungSol but I would imagine I would like it. Tried some other tubes but nothing else is noticeably better than 6L6. So EL12, TT21/KT88 and KT66 are my favorites. And I don’t buy any tubes that are not at least 40 years old, most of my EL12 are from 1954. EL12 is a good thermal fit for this amp, it runs much cooler than with big tubes like TT21.
More important than output tube is E80CC input tube. I would take E80CC with 6L6 over any output tube with 12AU7. And as you can see in the pictures I power the whole thing from a beefed up transformer (not just higher current rating but bigger magnetic core) with additional caps for smooth power delivery with ample on-demand capacity. And all other components are upgraded including all caps, almost all resistors, and the pot. And soldered with lots of lead and silver throughout.
I mostly use the amp with Schiit Gungnir Multibit with USB buffer. And 8500 with Mullard 12AT7 in between, cranked up to boost second harmonic. When I use turn table it is hooked up via 8500 too which has significantly upgraded phono section.