Which tubes are the best?

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.

My new Amps came with two quads of NOS Mullards EL34.  I loved them so much I started replacing the rest of my system with NOS Mullards - preamp NOS 12AT7 and phonostage NOS 12AX7.  They are as you described in your post- liquid smooth detailed rich. Easily heard the improved difference from the stock tubes the manufacturers used.  

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.

This is why tube rolling is such a waste. For every set of tubes you try the one thing you know for sure is you are out the money. They may well wind up being worse than what you already have. Now you have an extra set of tubes sitting around you don't want to use except for spares. So what? Are you gonna roll the dice again? Just how many spares do you need?? When that same money would buy a new fuse, or maybe a few, or some PHT if you have a turntable, HFT for sure (everyone has a room) or heck Nobsound springs, or even the really crazy good Townshend Pods could be had for what some sets of tubes will run you. All of these guaranteed to elevate, and with zero risk any of them goes bbbllzzzlzlzlsalzlzl SNAP in a blaze of glory like lets face it tubes can do. 

But hey, if you are "that guy" then at least do it right, give Dave Thompson at Raven Audio a call, he totally knows tubes, killer selection too. Can't guarantee he sells if you don't have a Raven, but I bet he would steer you right.

Tubular1- For those that like the JJ tubes - what is it that makes them good? Alos, where do you buy them?  

JJ are just as detailed and extended, yet just a tiny bit more liquid, which adds up to a bit deeper and more palpable sound stage. Compared to what? Tungsol, Gold Lion, ElectroHarmonix, and especially compared to the worst of all time, the only tube so bad I would say AVOID because literally 3 out of 5 failed spectacularly and within barely 2 months (!) tubestore.com "Preferred Series". Preferred?!?!? As compared to a root canal - maybe!! 

Oh well, they did honor the warranty- and gave me some credit when I said you know what, I am just not willing to risk tubes this bad in my amp unattended, which makes them totally unsuitable, so how about give me a deal on the tubes I know are good: JJ. And they did. And they are in there now, year and a half later, and still sound great. Just ask the guys who were here last Saturday.