Best sounding 6SN7 VT231 for amplifier input

I'm using Sylvania in my SET amp. They sound great. I think Sylvania has the most transparent and twinkly high end.

in my amp:

--Kenrad (vt231) black glass = BIG, lush sound (but still open, unveiled), bass bloom, music full of weight, the BEST in my amp (but NOT in my preamp!)

--sylvania vt231 = sparkling (like TWL said... "twinkly") up top, crystal clear, extended

--sylvania 6SN7W (NOT the metal base) = also transparent, a little thin, tight bass

--tungsol, blackglass round plate = neutral, balanced, SMOOOTH (perfect in my preamp)

RCA grey glass vt231 = lush, but also veiled/dark

national union black glass vt231 = very similar to kenrad, but a little more veiled (still very good)

GE 6SN7 GTA = good all-around neutral tube, much better than stock/chinese tubes, nothing totally outstanding about it

Define "romantic".....

For a VT-231.....

The RCA have a rich harmonic structure;
the Ken-Rad great bass and drive;
the Sylvania a wide bandwidth and excellent air;
the Ratheon are the sweetest;
the National Union have great midrange...

The most "balanced" of all these factors (and others) taken together is probably the Tung-Sol. I agree with DennisTM that this good balance/neutrality makes the Tung-sol a good preamp tube.

For the 6SN7W mentioned.... in addition to the metal base types, there are short and tall bottle 6SN7W tubes. The short bottle have better low level detail and the tall bottle more slam.

After trying out various WWII era Sylvania, RCA, and clear glass Ken-Rad VT-231s, I finally plugged in a newly acquired matched pair of black glass Ken-Rads and they have literally transformed my system.

They don't have the same top end extension as the Sylvanias, but I feel they have a more "correct" and liquid treble, lush mids, and solid bass. Bigger soundstage too.

My preference was the 6SN7W metal base, followed by the Ken-Rad and Tung-Sol black glass. The Mullard CV had a little higher noise floor, but very seductive and enveloping. When I wanted to simply float away on the music, the Mullard was a great choice; but just a little too romantic for serious listening. Enjoy.