As other's have posted here, and I'm appreciative of their comments, each tube make and vintage will usually supply a different flavor.
As for hours? outside of the Amperex & tungsol tubes rolling in new ones every other year of usage is a very nice thing. Not necessarily a needed thing, just a nice thing. Fresh tubes from a great vendor whose abilities to test thoroughly each tube sold is imperitive. i'm not keen on Audio tubes, formerly Brent Jessie tubes... BTW, Why the name change?
FYI ... His return policy bares greater investigation.
Andy Bowman of VINTAGE TUBES isn't the cheapest place to buy tubes, but I've never had to return any to him either. that's very important. Very. I'm sure too, if one did fail outright soon after receipt Andy would take care of it. Great guy, and excellent products.