I have a JJ 6L6GC in there at the moment and have been using that for the last 6 months, it sounds very good to me and I do push the amp quite hard volume wise, I bought a matched pair so I have the other in my guitar case as a spare. I don't have a stash of NOS tubes or anything like that. I do like JJ tubes they seem to be tough and sound good for a current production tube at a fair price. I did buy an EH 6L6GC a few weeks ago but haven't tried it as yet.
I do have a few NOS 12AX7's like RCA and Philips and I have tried them in my Tramp but I have a JJ in the preamp spot as well at the moment and I didn't hear a night and day change in tone, if anything I think the JJ might sound a bit smoother in the top end.
Snowy