I never owned an M8 but M9. I purchased a mint MP240 about 15 months ago and really enjoy it. Leica finally entered the modern digital age with the M240 with live view, focus assist and video.
The worst criticism of the M240 that I hear is the thickness compared to a film M or even the M9. This does not bother me as I presently use an M5 as my film Leica. I have been happy with the MP240 and it will go with me on a six month trip around the world this fall. The M10 does not tempt me at all although a mint M4 is calling my name.