The Older Mac's and Marantz Tube Amps. Today I would think stuff like Theta Dreadnaughts, Plinius Odeon and any amp that brings out the best traits of your particular speakers I would keep until one of 4 events occur.
1-Your Death!
2.Change of System speakers
3.Find a better synergistic match
4.They have a failure which puts the, out to pasture
1-Your Death!
2.Change of System speakers
3.Find a better synergistic match
4.They have a failure which puts the, out to pasture