"tube watts" versus "solid state watts"

2 amps with identical RMS ratings will probably have similar drive characteristics into a resistor.
As soon as you start driving complex loads with current ahead or behind voltage, that's where you'll start hearing significant differences.
Amps which can tolerate such complex loads will have more apparent power.
As a test you could find 2 different speakers of similar sensitivity..make them 91 to 93db rating. Also, 1 speaker should be a fairly benign load and the other as wretched as you can find. Huge phase angles and large impedence swings.
Try a couple or more amps. amp#1 should be a very high quality unit. Nearly any of the 'biggies' should work. Find another amp of similar power. This one should be of much lower quality, but similar RMS power rating. They should both play an easy load to similar loudness levels. However, when driving a difficult load, the better amp will play louder, longer without heating, and provide a much superior listening session.

Distortion usually increases with demand. More Watts = less clipping. Having more Watts, lessens the chances for distortion. On a cost per Watt basis, ss usually offers more Watts for yer dollar than tubes. One could argue that avoiding distortion is preferable to accepting more pleasing distortion. While it's an old fashion notion, and certainly not the end all towards choosing an amplifier, perhaps we should re-consider $ss to $tube Watts as part of this discussion.

To me,most tube amps seem to sound like they have more power than a SS with equal power.Also if I remember right,tube amps have even order distortion vs. odd order distortion put out by SS amps.This may already have been mentioned.

I think it has to do with the tubes warming up the hair in your ear. The vibrations of the ossicular chain displace the basilar fluid in the cochlear, causing the hairs within it, called Stereocilia, to vibrate. Hairs line the cochlear from base to apex, and the part stimulated and the intensity of stimulation gives an indication of the nature of the sound. Information gathered from the hair cells is sent via the auditory nerve for processing in the brain. That's why men love tubes.

It's not a tube vs transistor issue. I've had numerous amps all rated for 100W both tube and SS. Some sounded like kilowatts, some sounded like milliwatts. Some were just not a good match for certain speakers. Just trade-offs in the design/price. I could be more specific with the individual models but that would serve little purpose and be misconstrued as criticism.