who makes the best kt88 tube

Who makes the best KT88.. MO Valve/ GEC, of course.. there are no better than the originals..Of course they are VERY expensive, and hard to find, best source I know of is Andy Bowman at Vintage Tube Services.. http://vintagetubeservices.com/

Or is your question who makes the best current production KT88, well the most expensive are, as was pointed out the EAT tubes, the Psavane chinese tubes are pretty good as are the Gold Lion Russian reissues.

A sleeper - Shuguang GEKT88. Inexpensive, too. Buy them at www.goodcomponent.com. They are not flashy, but they remind me very much of GE6550A @ about $63/pair. Shipping from China is very fast by this dealer.

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

I'll be watching this thread with much interest...so far I'm using "plain ole" Electro Harmonix which are doing a very nice job on my bass amps (they replaced SED Winged C 6550's).
Thanks

Psvane T series premium grade tubes seem to be better option of the series.

Grant Fidelity has great information on the BB tubes which sometimes on other websites if shopping for tubes can be a mystery.

For other options checkout tubedepot for Genalex NOS KT88 tubes and other KT88 tubes options.

In my opinion the EAT KT88 Diamonds. I haven't tried the Treasure Z's or Psvane. The original GL Gec and Genelex are indeed hard to find and when you do the price is the same or higher than the EAT's.
Here is a pair
http://www.audiogon.com/cgi-bin/cls.pl?accstube&1330013434&/Genalex-gec-nos-kt-88-kt88-pai