The, "best" will depend on your tastes in presentation. For me, that's been the 40's Tung-Sol round plates, of the construction shown in this guy's pics: (http://cgi.ebay.com/TUNG-SOL-6SN7GT-OVALPLATE-VT-231-NOS-RARE-6SN7-/390169929815?cmd=ViewItem&pt=Vintage_Electronics_R2&hash=item5ad7f0a857), and not the mouse eared or round mica top support. Those combined with 1940's Sylvania 6SN7W or A(tall bottle), as driver and phase splitter- repectively, provide a very transparent window to the music(modded Cary SLM-100's). Some of the other top-notch tubes available, on the NOS market, are mentioned here: (http://www.dehavillandhifi.com/6sn7_vt.htm) If you like a warmer presentation; the RCA, Raytheon and Nation Union VT-231's listed will give it. All the best are bottom gettered(but the Sylvania 6SN7W) and will provide a nice open sound stage, and good imaging(if your system/ and room are up to it). Less salty in price, but still very clean and open(somewhat less sound stage width and depth, than the TS-rp & Sylvania-W though), are the Ken-Rad and Sylvania VT-231's. I've got some of those as back-ups, for when I can't afford to spring for the others any longer.
