This has been covered in detail both here and @ AA. Suffice to say these are the facts:
NOS are better, in basically all cases. (I have come across one new production tube that betters any NOS version, but that's it. And I have thousands of tubes.)
The quality of NOS will never be equalled again, for many reasons.
The prices are going to continue to go up, for NOS stuff. Every day there is one less mullard/amperex/etc. in the world - but never any more new ones.
Newbee, this is an uninformed opinion: "tube design is fairly well settled - not much new coming along." I have to disagree on that. There's quite a bit of new development going on in tube design. You won't see it from big commercial manufacturers though. It's all happening at the one-man-band level. Some of these things are new, others are re-discoveries of things known and done back in the 1920s and 30s and revived for modern use. But in fact I think if anything, more, not less, development and innovation is happening in tube audio than SS amps. The few 'new' things to SS are: The advent of so-called digital amps; Increased use of switch-mode power supplies by more manufacturers (not really new, just more in vogue now), The Gaincard (chip amps); and The Aleph line from Nelson Pass (among some of his other innovations). These are the only things I can think of in SS recently that can be considered somewhat 'new' at all. The 'new' things in tube audio are numerous enough that I don't have the energy to write them all down (and even then I am sure I'd miss some, there is so much.)
FWIW,
-Ed
NOS are better, in basically all cases. (I have come across one new production tube that betters any NOS version, but that's it. And I have thousands of tubes.)
The quality of NOS will never be equalled again, for many reasons.
The prices are going to continue to go up, for NOS stuff. Every day there is one less mullard/amperex/etc. in the world - but never any more new ones.
Newbee, this is an uninformed opinion: "tube design is fairly well settled - not much new coming along." I have to disagree on that. There's quite a bit of new development going on in tube design. You won't see it from big commercial manufacturers though. It's all happening at the one-man-band level. Some of these things are new, others are re-discoveries of things known and done back in the 1920s and 30s and revived for modern use. But in fact I think if anything, more, not less, development and innovation is happening in tube audio than SS amps. The few 'new' things to SS are: The advent of so-called digital amps; Increased use of switch-mode power supplies by more manufacturers (not really new, just more in vogue now), The Gaincard (chip amps); and The Aleph line from Nelson Pass (among some of his other innovations). These are the only things I can think of in SS recently that can be considered somewhat 'new' at all. The 'new' things in tube audio are numerous enough that I don't have the energy to write them all down (and even then I am sure I'd miss some, there is so much.)
FWIW,
-Ed