Which tubes are the best?

Hi folks, I just got a Muzishare X7 integrated amp. It is beautifully made and sounds like it has a lot of promise. Even though I'm just breaking it in, I am thinking about tube changes. Why? It's just what I do. 
I'd like your opinion on the best replacement tubes, meaning smoothest, most "tubby" and mellow tubes. 
I won't be chasing NOS tubes. I'd like your experience with Gelenlex Gold Lion, TungSol, Mullard, Telefunken, or?,  etc. of current manufacture. The amp uses KT88, 12ax7, 12au7 and CR34 rectifier. 
Any thoughts about KT88 vs 6550 would be appreciated. I used to prefer 6550 way back when. 
Any information would be appreciated. Yes, I could go through all the old posts but I do have vision issues after four operations and that's why I'm asking straight out. 
Thanks in Advance. 
Back in the day, I used to do some serious tube rolling. The absolute mellowest, most laid back and detail rich tubes I ever found were some Mullards advertised in the back of Audio magazine. They had Magnus Organ printed on them. They were amazing. Unequalled. Ten years ago, I was cleaning out stuff and took a box of my small tubes to a local dealer. Some guy gave me $350 for them. Wish I still had them heh. 

Groove tubes from brent jesse tubes.

EL34GT as they are made to be a close copy of Vintage Mullards. Brent mostly sells NOS and doesn’t like a lot of new production tubes but he signs off on these. That itself should say something.
The only tubes I roll are the signal tubes and the only tubes I use for my power tubes are Genalex. I have three different amps and all of them have either the EL34, KT-66 or Kt-88 tubes
Might check the provided link below. I found it to be helpful and reasonably accurate in tube gain. Like millercarbon said, it can get expensive. I was looking for more high frequency detail. I found new production Mullards to lack the dynamics I wanted. I have Bob Carver mono blocks that use KT88s. Purchased used. Previous owner had already upgraded the tubes. The KT88s were Gold Lion. The 12AX7s were some old stock Millard medical grade tubes. After rolling tubes, I ended up liking the sound of new production Gold Lions. Actually have replaced the tubes in Manley Chinook with the Gold Lions as well. The Gold Lions have more gain at higher frequencies. Hope you find what suites. Happy Listening!