I have 6bq7 from RCA and Westinghouse. I prefer RCA (slightly warmer) to Westinghouse. For some reason, Westinghouse offer wider stage, but not much depth. I prefer 6n1p variant to both 6bq7. I used to have pearl cryo 6n1p Reflektor from partconnexion. However, it develop noise after 2 years of use. So I order another one from partconnexion, and received one 6n1p-EV, but different brand from Voskhod. However, this tube was bright, so I decide to find one from ebay (not cryoed). I found the one that I like (similar to Cryo Reflektor) which was Gold 6N1P-VI. I remember paying around $18 for 4pcs.
For 5u4g, I only have experience from RCA 5u4g and GEC/Osram U52. U52 just much better that RCA 5u4g. I was lucky to have 2 u52 locally at my local forum in aus for quite cheap. U52 offer expansive stage and better bass texture to 5u4g RCA.
For 2a3, I would be interested to learn NOS tube. My experience so far only with new tubes from shuguang, sophia and full music. So far, I prefer mesh sophia (nice tone, big stage, great bass ext). 2A3-Z from shuguang is nice, but low bass extension is lacking (I read on hf, the 2a3-t one not much better than 2a3-z, but please correct me if I'm wrong). Full Music SE is nice as well, particularly in decay and texture, but losing to mesh sophia in staging. Stock 2a3 from Donald actually is really nice. I prefer it to 2a3-z with hd800. It's fun and raw presentation, kinda remind me of vali with better staging and bass