In all honesty tubes are all over the map right now especially given the state of the tube industry.
You really need to consider a few things:
1. sonically what are you trying to achieve?
The tube in the Synergy or whatever chassis you plug your modules into is actually the V1 input tube. This is usually the most important tube in the entire signal path and has the biggest impact on tone.
2. Are you after something current production or old stock?
Usually getting good, reputable, well tested old stock tubes is a lot more money. I could suggest tons of great NOS/ANOS tubes to you but without a good frame of reference it’s hard to say if it’ll work for your expectations and all of your modules.
Likewise the same is true of current production tubes you’ll be best served be a dedicated tube dealer that really sorts, screens, tests, etc.
in my experiences the reissue Tung-Sol tubes are all over the place and wouldn’t be my starting point.
I find that overall at least with where I source tubes JJ ECC83S Slovakian and the PSVANE 12AX7 Chinese tubes are most consistent, sound best, and are usually the easiest to source currently. Assuming they function well these would be the two starting points I’d suggest.
Really anything from Russia (new sensor which is reissue Mullard, tung sol, genalex gold lion, Electro-Harmonix, etc) are all over the map and **** near impossible to source right now due to the Ukraine invasion creating a huge supply issue. They also have a huge price increase due to tariffs and if you find them anywhere it’s likely not a reputable music dealer or tube store because believe me we can’t get them since selling out. Many of those Russian made tubes are also terrible choices in your modules cathode follower spot, like the tubes can pretty much fail instantly in that spot.
In my opinion to be as objective as I can if you have well screened and tested current production tubes from Slovakia you are probably good but reality is that tubes will never be what they once were the music industry is a niche market. Back in the 50’s-70’s tubes were employed in many industries including military/government use so tons of money, state of the art equipment, research, etc went into making them. Many materials and construction things were done in the golden era that simply can’t be done today due to environmental issues, cost, etc. obviously I’m not implying that all old tubes are superior or that all new tubes are inferior. Simply that tubes throughout history don’t have a definite shelf life and really you’ll benefit from good screening and selection. But if you can find the right old tubes some of them can sound much better and be way more rugged and longer lasting. After all things like JAN (joint army navy) tubes really don’t exist in current production.
Any tubes you buy today are really only being built in three factories that I’m aware of PSVANE in china, JJ in Slovakia, and New Sensor in Russia. Companies like Groove Tubes, TAD, Ruby, Mesa Boogie simply source their tubes from those factories and “screen” them and relabel them if they “pass their tolerances/specs”.