I did my degree from 1968 to 1971 and in the first year we did little else on the circuits side except valves and we built valve amplifiers for fun. The following year we did transistors and built transistor amplifiers.
We did lots of comparative testing (for fun) and there were people who liked the sound of valves and people who liked the sound of transistors. (It was complicated by the old class A / class B controversy too.) I was a transistor man.
People often described the valve sound as "warm" (which I think is like CNo's "liquid") but to me it is fuzzy. People often described the transistor sound as harsh but to me it is accurate. The truth is that both types of amplifier introduce distortion to the signal and it largely comes down to what type of distortion you prefer.
So the only way to find out which you prefer is to listen!
Chris