What's better 100w class a or 200w class ab?

I would have to agree with Audiomax....current drives the loudspeaker. Amperage, not wattage is the key. I have heard some rather gawdawful hi-wattage amps, and have also experienced the fidelity and depth of sound that that a high-current, though lower wattage device can provide.

If you can, try to listen to both amps under identical conditions...same program material, same preamp, same cables, same speakers. That is, if you can... this is not a perfect world.

Try to find out the output at clipping. There are a lot of amps out there that will drive demanding speakers at > 4 ohms continuous output. The question is: how will it handle the short term dips below 1 ohm? Regardless of impedence ratings (which are at continuous output), all speakers will provide short term loads of under 1 ohm (drum beats, bass plucks, etc).

I just upgraded from a Plinius 8200 (175 Watts into 8 ohm) to a Plinius SA-102 (125 Watts into 8 ohm). While the 8200 is a great amp for the price, the SA-102 is heaven. According to the Plinius US Rep, the 8200 pushes about 1000 watts at clipping and the SA-102 pushes about 4500 watts at clipping! (my numbers might be off a bit, but they are in the ball park) When I installed the SA-102, the difference in slam, speed, bass and overall speaker control was dramatic.

What I don't understand is whether the increased capacity of the class A SA-102 is due primarily to the class A electronics, or are class and capacity independent specs?

As an electronics engineer, I ditto Sean. There are few only class A amps out there and virtually none will do 100W in class A. The problem is the BJT saturation currents on the load line. The higher the bias, the smaller the swing allowable and hence the sooner the need to go class B, otherwise your THD goes up several hundred percent. Class B is generally twice as efficient as class A so heats the room half as much.
Capacity on the other hand, has very little to do with class circuit topology. It is dependant on number of BJTs handling current and their ratings. Class B has better current gain than class A but with the right transistors you can do the opposite. Take care. Arthur

An amp with very high rail voltages that is capable of sustained amounts of high current would be best and most versatile. Some loads REQUIRE both aspects for best results. Such a design requires quite a bit of heatsink area though and is not cheap to produce in terms of transformer and amount of output devices. Don't under-estimate the importance of rail voltage in a power amp and simply look for something that is supposedly "high current". You might find something that sounds good, but it would limit what it could be used with in terms of future speaker purchases. Sean
>

If you need the power due to inefficient speakers, lossy room and/or high desired listening levels then the higher powered class AB might be better. If you can easily reach desired listening levels in your room with your current equipment and 100 watts of power then you might prefer the lower powered class A amp. The class A amp will probably use more electricity, require more space (may require different cabling) and create more heat.