The biggest factor is the player. Get six people to play the same piece of music with the same guitar and amp and you'll get... six different sounds!
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Thats a very interesting comment. I may try that one day and see what happens.
By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.