Your ears is the standard. Do not believe any tools as till now there is not such tools can tell you which is better or worse.
Tube vs Solid State Amp measured with REW
I have both a tube amp (Masterworks SET 300b) and a solid state amp (Arcam A32), with Klipsch Forte 4 speakers. The Masterworks sounds much better; more clear, very lifelike. But when I measure with REW the frequency response and THD are about the same (albeit with some variations over the range). Is there any other parameter that causes one amp to sound better than the other, that doesn't show up on the measurements?