Which tubes are the best?

JJ KT-88s are quite nice and hold up well too. They make some upscale versions like the 'blue glass' that seem to be worth the slight extra dollars. The Chinese make a very nice 12AU7. I avoid 12AX7s in my designs so I can't comment about that one. But we've had a lot of nice feedback on the Psvane tubes, and also some nice comments on the Gold Lion (Russian made) 12AU7, so those might be good places to look for a 12AX7 that isn't NOS.

With my Ayon Spirit 2 I prefer the sound Gold Lions or Psvane KT88s to either the clear or blue bottle JJs , but you need to try tubes for yourself to see what sound flavor you like.That amp takes 4 12Au7s , I use two NOS RCA 12Au7s blackplates, and 2 RFT ECC82s.

I have 2 other integrated amps that use 12X7s, in my Line Magnetic I use NOS Tungsol 5751s to reduce the gain a little; in my Finale Audio I use NOS GE 12ax7s

To my ears changing out the respective JJ , Electronic Harmonix or Chinese signal tubes that came with each amp took the sound to another level; worth the expense

For those that like the JJ tubes - what is it that makes them good?  Alos, where do you buy them?  

I get mine at TubeDepot.com.   Not sure I notice worlds of difference, but JJ's aren't very expensive, sound fine to my ear, and have a good reputation, and at least the ones I've bought are not over-priced for what my ears can hear.

Tube rolling can be fun, rewarding, and expensive!

I've got a PrimaLuna Dialogue HP Integrated; your Muzishare X7 seems to be of similar design so I'll share where I've landed.

Disclaimer, I've got XStatic electrostatic speakers combined with a bit of age-related loss of high frequency hearing so I tend to like slightly brighter sounding tubes in my PL.   YMMV...

I'm running 8 Tungsol KT150 power tubes.   This was my first big upgrade from the stock PL EL34 tubes.   This brought out much more depth and punch to the bass while still preserving the warmth of the midrange.

I played around with the 6 12au7s and my favorite combination at the moment is: Radiotechnique in the center preamp locations with the Gold Lion's just outside of that.   The Cathode followers are NOS RCA Cleartops.   The Radiotechnique are definitely on the bright side so I may swap them with the Gold Lions and give that a whirl.   These changes significantly increased the high-end extension and energy bringing a nice balance to the overall presentation.

It is remarkable how you can fine tune the sound by swapping tubes.  You can't make a bad device sound great with just tubes, but its all part of the complex system to tweak it to your tastes.

Not trying to hijack this, but don't forget to try a different fuse.   The SR Orange change was also noticeable.   I describe it as making the black parts of the music blacker thereby letting the instruments stand apart and increased the detail.   Electronically, perhaps it just lowered the noise floor?   I don't know, I just liked the change.

Enjoy the experimentation and don't forget its all about the music and your ears.