IMHO, I believe that an amplifier is mated to upstream componenets and downstream (speakers) components, which play a huge role in how the system will sound. I have had several good amplifiers in my day which have sounded marvelous with one set of speakers (and room placement), and dry and lifeless with another. So . . . I guess it depends on the gestalt.
what are some of the best amplifiers
I have owned many amplifiers over time. Some were high priced and some were not. My latest finding is a pair of Forte model 7 monoblocks reworked by John Sodderberg. These are very magical amplifiers after 1/2 hour of warm up. The midrange is the best I've heard. Full bodied yet detailed. There is a mystical ring of air and depth that has to be heard to be believed. I have owned Threshold amplifiers(Fortes maker) and feel that the less expensive Fortes(4a and 7's), even in stock form, outperform the Thresholds. I think less is more!