This has been asked before in this thread several times.
They are different beasts.. Depends on what you are looking for.
I have had both at the same time. Kept the M-Stage, sold the O2. Never had an issue with noise with the Matrix. My issue was I found the O2 too sterile. Fans of the O2 will say that the Matrix is colored.
My experience is that you should take any recommendations for the O2 with a grain of salt. The fanboy club around the product tends to outshout those who didn't care for it. Everytime I say I didn't like it someone pipes in that I must like distortion and coloration. That is not the case, I just like to enjoy my music rather than revel in how true to the source my amp is. My music, my tastes, my gear. my opinion. Yours may vary.
Now, just watch the reaction....
My reaction.. very well put. This is why I personally went for the M-stage rather than the O2 when I was deciding between the two.