who makes the best kt88 tube

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

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.

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