6SN7 - Same tubes or mixing with different kinds?

What is more preferable?
I see most tube gears are shipped with the same kind tubes, but I came across one claim that combining different kinds would be actually better.
From tubeseller.com:
One thing became clear based on customer feedback, combining 6SN7 types seems to work better than using all 6SN7s of the same type. With so many preamps and amps using this tube, you can end up with Six 6SN7s per channel. It appears combining tubes like the VT-231s as voltage amplifiers and 6SN7Ws or 6SNGTA/GTBs as driver tubes you gain the strengths of all. Using one type seems to accentuate the tube’s weaknesses.

Has anybody tried with combining various 6SN7 tubes? Like mixing GT, GTA, GTB, 6SN7W, ...? If you have, have you tried mixing different brands? Any positive experience?
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I used to own a Cary SLP 98 preamp that used 4 x 6SN7. Two were used as drivers and two were used as output buffers. I used the same, as well as different matched pairs in each position. My favorite combo was the Raytheon VT-231 in the driver position and Sylvania GTB in the buffer position.

Try the link below which provides an inventory of 6SN7 tubes, their sonic characteristics, and in some cases use preferences put together by Dennis Boyle of Chimera Labs: