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

I would go for 200w class AB as long as you have at least 8-10w Class A....If the 200w amp has less than that it will likely sound bright after it blasts through the class A region and say a female vocalist is screaming away at the top of her lungs....We at CTC just finished a huge mono amp which runs over 25w class A and, other than running at over 50 degrees C, it measures beautifully when in the class A region with just 2nd and 3rd harmonics and starts picking up some 5th as it crosses over into past 25w up to 400+w or so.....Lots with tradeoffs in amp design and hard to get everything right so we concentrate on the area at 10w and under where most all the music, other than atomic blasts, will be played.....

I'd reckon that the biggest question is what is the impedance of the speaker? Since this fellow is deciding between two amps from the same mfr, the biggest diff will come IF the "class A" amp slides into AB because of a low Z load. In which case it might just put the same power into the load as the AB amp from the same mfr.

The circuit is likely to be identical, just the rail voltage will change - assuming the description is accurate, the 100w class A amp *ought* to have *higher* rail voltage than the 200w AB amp -as the load causes the amp to slide into AB the advantage of the higher rail voltage will be more output available than with the nominally higher rated 200W AB amp!

:- )

Of course into a calm 8 ohm speaker - go with the 200 watt AB, IF the criterion is only max output with an inefficient speaker...

It also matters what the output devices are. Mosfetters and BJTs act a bit differently in AB vs. A.

On the other hand, with two amps that use the identical circuits, I'd pick the one with the better power supply regardless... :- )

_-_-bear

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Despite all the well-intentioned responses dealing with the theoretical above, I have to agree with Seandtaylor99. You already have your speakers chosen, so your mission is quite clear: find the amp that sounds best with your speakers. If you've already determined that Lamm is the brand you're most interested in, then you need to try and audition both the amp models in your system. One of the two will no doubt win your preference. Nobody should have to drop the kind of bucks these electronics cost without being able to hear them at length at home first. (You might also pose your question to the respective manufacturers of your speakers and desired amps just to get their takes on the issue, but you'll want to be prepared to give them more info than you've given us, such as room size, ancillary gear and cables, musical preferences, and listening volume preferences.)

If the FIRST watt is not RIGHT, why bother!!!

Interesting point Audiomax. Too bad more companies don't print max current. Creek would advertise peak current of over 30 amps I think but never in their specs. I can subjectively agree with Drrdiamond about Krell as their integrated is punchy.
Musical Fidelity now publishes this info:

A3.2 integrated 115 watts: peak to peak output current 24 amps.
A3.2 power amp 130 watts:72 amps
A308 integrated 150 watts: 48 amps
A308 power amp 250 watts: 72 amps
From listening, the higher current gives a crisper sound. Also there is more detail possibly because the high current fully magnifies every small detail.
I can also subjectively say going from N804 to N802 and ATC active 20 to ATC active 100 the bigger speaker presented more detail. Again, I think because of the higher power and ease of presentation that a larger speaker can do.
This is all a little off track but hopefully interesting.