Best sounding 6SN7 VT231 for amplifier input

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.

The final choice of course comes down to your system and your personal taste. This list should keep you busy for a while! :-)

Mixing tubes is done by many people. Try the VT231 as voltage amplifiers, and then maybe some GTA/GTB's as driver tubes.