Best 300B tube for Cayin 300B amp?

Calloway, what amplifier(s) are you using with them? Since the OP stated their amplifier of choice for usage in. I recently bought a barely used matched quad set of "royal princess" for use in my Wavelength Cardinal XS amplifier pair.
Oceanica, My amplifiers are too recent to me to have tried different tube pairings, tho, I earlier purchased a pair of Shuguang Black Treasures. I have no complaints with either, but have been too busy enjoying the music to exchange for an attempt at a comparison. I suppose this was not much help:) Interested in your future findings.

Clarification: Wavelength Cardinal uses one single 300B per mono amplifier. Pair in use and back-up pair. Nice:)

isochronism....i have chalice audio 'grail' SET monoblocks...chaliceaudio.com...the 300B tubes..1 each amp..are the driver tubes in this configuration...( see pic in my 'system' area)..the 'royal princess' tubes are not cheap...~ $ 1200 / matched pair...but they are much better then the sophia 'princess' tubes they replaced and worth the price..hope this helps..dave

Occanica,
You don`t mention a price range,300bs can cost anywhere from 150-2000 USD.A competitor to the Royal Princess in it`s price range is the Takatsuki TA 300b(Japanese).
EML XLS and mesh 300b are very well regarded.

I`ve been using the Shuguang Black Treasure for two years and it sounds fabulous and has been absolutely trouble free. For 600 USD they`re worth every penny.
That new Takatsuki is very intriguing.

Ocenaica, the fact of the matter is that there is no set answer. A while back the choice was clear, if you had the scratch - Western Electric. Now there are several contenders at the top - those mentioned above and a couple of others - as well as some good second tier ( and much more affordable) options. In my opinion, if you can resist thinking of it as a lot of money for tubes, but instead view the expense only as "bang for the buck" improvement of your system, compared to the expenses of all your other components and ancillary equipment, the best are well worth it. Which of the best is the best for you? That will be determined by your personal taste and system synergy. I’m very happy with the Royal Princesses.