best vintage 70s, 80s amp?

One of my favorites from back then is the Mission 776/777 combo. No detail by modern standards but punchy as Cassius Clay (time appropriate). Combined with Altecs or Klipsch horns, it could hurt you. Ahead of it's time in many ways. First battery powered preamp.

There were some rare Yamahas and Kenwoods that broke through the consumer electronics barrier but beware of obsolete FETs.

That's easy... IMHO it is the ARC D70 in either Mk 1 or Mk2 versions.
I used to own a Hafler DH220...NOT even in the same league as the ARC.
The ARC is one of the best tube amps I have heard and i believe it will stand up against most any tube amp, even by today's standards. May want to read my review in the review section for more info.

What speakers will it drive? How big a room will it be in? Need more information in order to provide a recommendation.

Junglern what speakers will you be using?

Harman Kardon CITATION Series from Lee Kuby were very good. Circa mid 70's.

I had the CITATION 16 amps and the CITATION 17 Preamp. Still have the CITATION 19 power amp for my SUBS.