There is an openness of sound that tubes are capable of that transistors have not yet achieved.
The only real downside to using tubes in amplification devices is related to driving lower impedance speaker loads (4ohm and below). In a preamp, tubes can drive the high input impedance of a power amp, which is typically 20,000 to 200,000 ohms, quite easily. There is also no need for an output transformer in a tube preamp. All of this means that the preamp is an ideal place to take advantage of the sonic benefits of tubes with no real downside.
The best tube and solid state preamps are attempting to converge on the theoretical definition of neutrality, but they probably never will because it doesn't likely exist.
The only real downside to using tubes in amplification devices is related to driving lower impedance speaker loads (4ohm and below). In a preamp, tubes can drive the high input impedance of a power amp, which is typically 20,000 to 200,000 ohms, quite easily. There is also no need for an output transformer in a tube preamp. All of this means that the preamp is an ideal place to take advantage of the sonic benefits of tubes with no real downside.
The best tube and solid state preamps are attempting to converge on the theoretical definition of neutrality, but they probably never will because it doesn't likely exist.