RX100/mkII undoubtedly has better IQ than the M, but there are many people complaining about dust accumulating on sensor, even after few weeks of light use. Some claim they used proper casing to protect/carry around the camera. And the only way to clean sensor is to send it back to Sony or other repair shop. Sucks that in order to make the camera more portable, Sony resorted to P&S style lens instead of having a detachable lens like Nikon 1 system. Another con, to me is durability concerns. Everything about the lens is controlled electronically, from the lens cap blade to circling electronic dial around lens to control everything. it's just one of those additional things that can go wrong. In short, if Sony offered this camera with detachable lens and in camera lens cleaning mechanism, then I think the RX100 would have been even better. I guess Sony didn't want it to compete against NEX-5/6.
Fuji X100 and X M1 are great cameras with just as amazing IQ as the RX100. However their quality control is problematic. Even worse is their warranty repair/support here in USA. Based on what I read, it is horrific, in the true sense of the word.