I thought M1 is more analytical than M2, although M2 sound better over all. Am I wrong? So if you prefer classical music than M1 is for you.
Based on the reviews, I don't think you're correct. Especially read joker's review posted on the mp4nation blog. The M1's are more balanced, but by reducing bass - not adding treble. Joker commented that there's even less sparkle in the high frequencies than with the M2. So I still wouldn't recommend them for classical.
based on what i've read both here and over at head-fi, it seems the M1s have a more punchy bass while the M2s have a more full boomy one by comparison. (I tend to prefer punchy to boomy)
The M2s however have been described to have a more thicker creamier sound while the M1 are a little more flat, but not by enough of a difference that most people wouldn't be able to tell difference unless side by side comparing them. These seem to be the major differences as far as I understand it.
Currently I am leaning more towards M1, due to the punchy bass, less fatiguing over longrun, and the more balanced sound overall, since I listen to a wide range of music styles, and it was stated that the M1 does do well still with bassy tracks like D&B and rap.