Most amps that are rated for Class A operation are actually AB. They stay in Class A much longer than normal, so they refer to them as Class A rather than stating "VERY rich Class AB". Very "rich" AB amps stay in Class A for anywhere between 8 - 30 wpc ( some go a little higher ) before switching over to Class B operation for power levels beyond that point. To dissipate BIG wattage and run Class A would take MEGA heatsinking and forced air cooling if you were standing on the throttle for any amount of time. You will realize just how much heat you have pouring off of one of these amps as the ambient air temperature of the room will climb quite noticeably.
As to whether it is important that the amp stay in Class A for a long time, some people say that Class B sounds better. While there are technical reasons as to why this would be impossible, my ears tell me that the higher the amp is biased, the better it sounds. Keep in mind that high bias amps typically require very long warm up periods to sound their best and typically perform optimally after being on for quite some time. As such, i don't shut my amps off as i've found them to really "sing" after being on for about 2 - 3 days or so.
As to your original question, unless the circuits were identical and you knew the point that the amp switched from Class A to B, there really is no "best" answer. Sean
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