Tube (Valve) Health

[mmd]

I have two sets of tubes for my headphone amp, but I'm stuck figuring out how to measure which tube is working better.

1945 JHY-6AK5 Hytrons (Army and Navy Grade) tubes which HAVE seen war use in a portable radio.

1957 6AK5W Philco tubes (never used).

The hytrons sound CRISP and clear, but their bass has slowly started fading away but still sound clean.

The philco's have a strong bass response, but whenever anything bassy plays, the high and mid end gets distorted by it.  Also, one of the tubes seem to have more bass strength than the other..

I don't know which set of tubes to use. Or even, how do I know what they are supposed to sound like?

I thought about a burn-in period for the tubes, but I'm fairly certain the Hytrons have already been burned in.