NOS tubes

I don’t think that’s true freediver. Current production tubes are made in Russia and China and their construction is very different from the classic tubes made in the US, the UK, Holland, West Germany and many other countries. I’m not saying that they don’t make good tubes today, but they’re not made on the same equipment that the classics were.

There are cases of countries buying tube manufacturing equipment and using it after the original companies shut down in the 1970s. Ei in Yugoslavia bought Telefunken’s old equipment and someone in Japan ( Mitsui maybe?) bought some of Mullard’s old equipment and continued making tubes.

Some people prefer current production, I prefer the classics for the reason hifiman5 stated. Different brands have their own sound characteristics which can be used, along with other accessories, like cables, to tune the sound of your system. It’s just my preference. Some people don’t like to use tubes at all. They prefer SS.

To answer the OP's question.  And I'm talking about preamp tubes not power tubes.  Tube quality was very important back before transistors replaced tubes,  when tubes were used in essential functions in airplanes, radar, early computers, television broadcasting, medical equipment, etc.

They are getting better at making tubes but the really good ones often cost as much as NOS.  You would think that eventually they will make tubes that sound better than NOS with the technology available today, and I think they probably will, but for now I prefer old stock to the new production tubes I've had in my system.

What amp did you buy wow?  If you decide to start rolling tubes, it would be best to work with a good tube dealer (Brent Jessee, Andy Bouwman at Vintage Tube Services or Kevin Deal among others) rather than try your luck on ebay.  They can offer educated opinions on which tubes might work for you and you can trust that you are getting what you paid for.  It will save you money in the long run.

That's a nice amp wownflutter, but I can't tell you who would be the best tube dealer for you.  When you get ready to try rolling I'm sure there will be people here who will be happy to offer advice.  Enjoy!