6DJ8s - its funny if they tell you that older bugle boys are that much better insofar that they were developed in the very late 50s, so it's got a shorter age span. Though i'm sure the differences in construction among the brands become a big differentiator. When I used to roll 6DJ8/6922, while there were differences between the orange globe, bugle boy, and PQ types - nothing super huge in terms of SQ differences to me.
Me neither. 99% of the time "30s-early 50s" top "late 50s-80s" as far as most everything i've read for comparisons. I can understand this though as manufacturing and demand over time changes. Now, one of the tubes that nearly continues the similar quality throughout its lifecycle course to me is the Tung-Sol to Cetron 7236. I couldn't tell the difference between the two albeit the tube being a power tube for the DV.