In my opinions, forget the M. It is just too thin walled.
Also in my opinion copper is for homes of the past and there is no good reason to use it in new homes. Look at the posts here for frozen, burst, leaking, pin-holed pipes and the trouble most Diy'ers have repairing it.
PEXa or CPVC would be my choices now.
There is the argument that many have that they have done it this way for 30 years and nobody can tell them any different. That's all fine and dandy but I use a cell phone, or home phone, not a telegraph, a computer, not a typwriter, and tools that use rechargable batteries.