if there were a single 'best' tube it would make life so much easier ... but there isn't. there may be a personal favorite tube for a particular system & for a particular headphone for that system and for a particular musical genre, but that tube might be just so-so for someone else's setup. in the realm of 12au7 types, i continually refer to the rca cleartop, not because it's the best, but because in the world of nos, this brings tremendous value. what other very good sounding 1960's tube in nos or anos state can you get for < $8? for me this tube sounds very, very good whether i'm using my t50rp, hfi-780, rp-htf600, or superex st pro-b.
are there other tubes i'd like to get? absolutely ... how about telefunken ecc802s or dutch amperex 7316, all from the '50s or '60s. even mentioning these tubes makes my wallet sweat .. LOL.
did you happen to get a 1950's square getter, d-getter or halo getter hytron?
i like my raytheon 5751 windmill getter in my other tube amp, but there's also '60s raytheon jan-crp-5814a with windmill getter which would be interesting to try. so many tubes, so few $$.
best,