Which sounds best?
Problem we have is that tube amps are variable tone controls. They have variable frequency responses due to the output transformer and relarively high output impedance. This means they have a different frequency response with every different speaker you connect them to as every different speaker presents a different load. Just take a look at any Stereophile tube amp test.
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So it's a complete lottery what a tube amp may sound like in your system.
Any tonal variations may or may not compliment a speaker or recording.
It's just simpler and cheaper to use a graphic equaliser if that's what you want to do.
"Tube sound" is quite technically explainable.
They do distort more and change performance with wear and different replacement valves. So from a sonic point of view I think they are just a headache and not worth considering. A, random effects generator doesn't fit my definition of sounding better.
Aesthetically they are lovely. The pleasure of owning and using one may trump a person's desire for accurate sound reproduction.