In my opinion, the best "new" 6SL7 (and 6SN7) tubes are leftover Chinese military versions, under the Shuguang (not the current red or brown base) and Nanjing labels.
Both are metal base, have different sonic signatures, and available at low cost, even if the Nanjing are far more difficult to obtain for a Westerner. Not that this should make a difference, but I find the look of the Nanjing very nice; a shiny, silver metal base with a pretty cool logo to boot. For the important stuff, I think the Shuguang are better, but for one looking for a warmer, richer, fatter sound, that is often so very much needed to balance the sound of today's components, the Nanjing might be the better option.
Both are metal base, have different sonic signatures, and available at low cost, even if the Nanjing are far more difficult to obtain for a Westerner. Not that this should make a difference, but I find the look of the Nanjing very nice; a shiny, silver metal base with a pretty cool logo to boot. For the important stuff, I think the Shuguang are better, but for one looking for a warmer, richer, fatter sound, that is often so very much needed to balance the sound of today's components, the Nanjing might be the better option.