My M&P9c is currently riding in a Tucker Texas Heritage, which is a great holster. However, they're pricey and require a long wait, unless you can find a lightly used one for sale online.
I'm a big fan of that style of IWB holster with offset belt clips, leather backing, and adjustable cant and ride height. Examples of this holster include the Comp-Tac MTAC, Crossbreed Supertuck, K&D Thunderbird Defender, and Tucker Texas Heritage. They're all very comfortable due to the leather against your skin and the wide holster footprint, and most guns can be concealed under just a tshirt. Plus, with the adjustable belt attachment clips, they can be tweaked to fit any person's body shape and carry preference.
Of these holsters, the Comp-Tac MTAC specifically has a few big advantages, including a fast turnaround time of 1-2 weeks vs. several months for other holster manufacturers, the fact that it's cheaper than some of its competitors (especially with their current 10% off sale), and the ability to convert the holster to carrying another handgun by simply purchasing another $35 Kydex shell.
However, while the fit and finish of the MTAC is superior to the Crossbreed, it's not as good as some of the others. The other major shortcoming of the MTAC is the fact that it's only available for a relatively small number of handguns, when compared to the options available for other, similar holsters. But that's not an issue with the M&P (as it is with the S&W 3rd Gen autos).