Class A to XX Watts

Just how noticeable the transition from Class A to Class B depends on different conditions. Often times the transition will happen as either bass demands and/or overall volume increases. During such times ones ears might not be as sensitive to the change from Class A to Class B. Usually the longer an amp can maintain Class A operation, the longer the amp can offer it's contribution to better sound, but the longer an amp can maintain Class A, the more expensive and less efficient the amp becomes. Better to to switch to Class B than to run out of Class A Watts, and run into distortion and clipping. High biased Class AB amps can be an appropriate combination of sound quality, efficiency and economy.

Pubul57, unto itself that might appear to be the case, but speakers are another issue unto themselves. The net result of the interaction between them is not necessarily as it might so appear. Speakers that are less efficient aren't so for the sake of it, but for advantages elsewhere.

As the posters above wisely point out; there is more to making good sounding amplifiers than just Class of operation.