"The best" is of course a subjective judgement. Synergy is ALWAYS the keyword: what matches up with your source component, speakers, cabling, + your sonic preferences? Experimentation is the only real way to determine that.
I can vouch personally for the Accuphase P450 being a fantastic product (although Mosfet; it's not a class A output) the driver stage itself is likely approaching class A bias; many other amps do likewise.
I also have an Ayre V3 which *is* 100 watts true class A, fullly balanced, another great design. I believe they also made a V5(?) with more output power + pure class A.
I do recall hearing some Krell class A monoblock designs at audio shows long ago; they're very large + very heavy. Spectral is another great one from years past.
