I think that NOS tubes are better for several reasons:
1-many more tubes were used 50 years ago than today. This meant that economies of scale came into effect-it was cheaper to use good components if you were going to sell more.
2-Since tubes used to be the only option, everyone concentrated on just one thing, tubes. Many of the good NOS tubes were actually made for the military who had very tight standards for tube performances.
Also, from my experiences, many new tubes can sound quite good. Some are even copied designs from vintage tubes. Everyone seems to be trying to copy old Mullard EL34's. However, nobody seems to be able to copy the life span of these. Mullard and Telefunken tubes seem to outlast everyone's efforts-they must be built better.
1-many more tubes were used 50 years ago than today. This meant that economies of scale came into effect-it was cheaper to use good components if you were going to sell more.
2-Since tubes used to be the only option, everyone concentrated on just one thing, tubes. Many of the good NOS tubes were actually made for the military who had very tight standards for tube performances.
Also, from my experiences, many new tubes can sound quite good. Some are even copied designs from vintage tubes. Everyone seems to be trying to copy old Mullard EL34's. However, nobody seems to be able to copy the life span of these. Mullard and Telefunken tubes seem to outlast everyone's efforts-they must be built better.