There different versions "best" with regard to tubes. The most reliable could be the old genalec as many still work after years of use. Part of this is due to a well made tube, the other is their common use in mac circuits known for an easy tube life. Best sounding is in part due to the circuit they are designed for and varying plate impedance of the tubes. The ability to also set both dc and ac balance is critical.
Best sounding in my Quicksilver silver 90 are Tesla/JJ. Unfortunately, they have dropped in reliability. Mike Sanders has a good reliable supply, but they are not cheap. In my eico hf 89, the wc 6550 are great. If you need kt88, I like the kt 120 as they are very good. The eh kt88 are
also good, but a little darker. The genalec are good, perhaps the most reliable, but overrated, the best looking, just a little congested for me. The sovtek are also good, but bass is not tight. The wc kt 88 are flat and congested, very poor sounding. The chinese kt88 are very good in various versions. Try all you can....jallen