12ax7's

Fletchj is right on the money. I prefer the rich, warm sound of the Teles, personally. I've tried all the other mentioned above and I fully agree with Fletch's description. Cheers,

A 5751 will give a bit less gain, but it also has less distortion than a 12ax7. A much quieter tube.
RCA made a tripe mica version of this tube that is very durable and wonderful sounding. Look around for them.. well worth the effort.
mike

I agree with Fletchj and Detlof, it really depends on your taste and the circuit it's used in. The best 12AX7s I've found for my taste in Jadis equipment have been Telefunkens, and the best Tele's I've ever used are their premium E803CCs. Much quieter than the standard 12AX7s, and they last forever.

I've just put four Tele E803CCs in my Jadis pre-pre and they are indeed much quieter than the best of the normal ECC83 Teles I had used so far. They also seem to provide for an even better defined and tight low-end.

Much more transparent and dynamic in my JP80 and JA80s than the standard 12AX7s, as well. Obscenely expensive and very rare, but when you want that last bit of refinement they do deliver the goods. Fortunately you get much of their performance from many less costly tubes.