I'm looking to CC an M&P 9, but am undecided on how to carry. IWB? Shoulder rig under a shirt? I'm a typical middle-age guy with 25 extra pounds around the middle (5'11", 240 lb).
Try all your options. See what works best for you. Then practice from that carry method. Most likely it will be IWB or owb @ 3:30 or 4:00. But if you like a shoulder rig. Do it.
Until recently I CC'd my M&P 9c OWB. Even then I never really got used to the thickness of the M&P especially if it has the laser grip installed. It concealed good but printed easily also. I'm a large person and carrying the M&P IWB was just uncomfortable enough to convince me to carry in another fashion which is why I switched to OWB.
I have a Crossbreed Supertuck IWB and a SnapSlide OWB. Normally carry my 9C IWB but have carried my fullsize too. The compact is obviously easier to conceal, pretty close on comfort though.
I have big hands, and while the full size grip is more comfortable, the shorter grip really doesn't affect accuracy, nor does the shorter barrel. At short distances (~15y) I can shoot both equally well. The pinky is not necessary on the grip to maintain control, you just have to get over the mental urge to feel it on the grip. Hickock45 recommends sticking the pinky out even.
The shorter sight radius on my 9C makes it quicker for me to line up the sights. A capacity of 12+1 is more than most compacts, certainly more than "mouse" guns, which hold about as many rounds as a revolver. Having 12 rounds is very reassuring to me! Plus, I can use 17 round mags, that I can keep in my pocket or on my belt as backup. I most often just use full size mags just for target practice though.
My 9C has a safety, which I sanded down for IWB. It is quite comfortable even with the safety, and easy to conceal. The 9C has only slightly more recoil, and since M&P's have such low recoil inherently, it is still probably average (as opposed to the XD9C, which has notable muzzle flip).
I use a Dun Hume 715 IWB for my M&P9. The M&P9 is not a difficuly gun to CCW short of a tank top and beach wear. I also have used the same Don Hume products for a SIG 220, and Glock 27. I am in the process of getting one for my M&P9c.