Hmm. Got offered my choice of two barn-find cars. A '74 Firebird or a '73 SS Camaro. Everything is original on them but the tires.
If this were offered to me, first question I would have is the odometer. High mileage is a liability for any machine that's over 40 years old.
The choice of one 45 year-old amplifier over another will have more to do with condition than anything else. Too bad there's no odometer to read.
If the Phantom is the older 12-tube version, run don't walk the other way. It has a problem with destroying the High/Low relay, and it's the oldest version, to boot. If the "40-year tuneup" has been done, this would be a big advantage. If you make it a daily driver, any factory-original electrolytic capacitors will liven up your day when (not "if") they break down from age alone. If they have been changed out you won't need to.
I'm accustomed to seeing the two relays in the rear of the Varmints going bad after the first 30 years. The newest Varmint you could buy was 1979, so you're well past that 30-year mark. Same rule about electrolytic capacitors as for the Phantom. With one difference. The big high-voltage filter caps are probably concealed under a circuit board where you can't see them.
It's certainly possible that either or both 40 or 50-year old amplifiers will fire up and be a reliable daily driver.
The odds are not so favorable, though.
73