Stereo amplifiers are available in a barrage of types with vacuum tube, solid state, class A, class A/B and class D being the most common. To say, that one type is better than another would be a silly statement and somewhat like claiming that chicken tastes better than beef, pork or fish. It is simply a matter of personal taste. The fact is that the mode of operation will never make up for quality of parts and design. I can tell you that Class A is usually larger, heavier and more expensive and that vacuum tube units run hotter. Class D, on the other hand, is smaller and cooler and Class A/B is generally less expensive. Although the approach to amplification may be very different in each class, the end result can be strikingly similar. Many audio magazines reviewers have made a decent living by testing amplifiers and relaying their opinion to readers; unfortunately, this is just another person’s taste, he or she may too prefer chicken to beef, I do not. I suggest that you use the spaghetti sauce approach. I taste the sauce to know if it is good, to my liking. Similarly, to know if an amp is good I will listen to it. I realize that the ancillary equipment used by your dealer may be different than yours, and that the room acoustic may also be differ, but providing that these variables are the common denominator and the only change is the amp, the difference between two amps will become the constant, and therefore assumed valid.
Happy listening! Tasting!