> ...preamps with pentode or triode in the first stage preamp. Which sound with more musical harmonics.
The distortion of triodes and pentodes, at the signal levels found in microphone preamps, is not very different.
Distortion is affected much more by choice of voltage, current, and load.
Microphone signals are weak. Pentodes have more noise (hiss) than triodes (for similar operating conditions). Pentodes are not usually your first-choice for weak signal amplification. Yes, there are a few excellent pentode-input mike preamps, but they require careful consideration of noise problems.
In general, I think a mike preamp should just amplify, without adding "musical harmonics". You have one chance to catch a great musical performance: you want to capture it and record it exactly. Then you can play that recording through various "color" devices (distortion, reverb, filters) and carefully compare different sounds. If you add "color" in the initial recording, and later decide it wasn't the right coloration for that performance, you are stuck. (Many experienced engineers do decide to add color in the initial recording, but this requires great experience and judgement.)