"Best" holster is a subjective term, while I'm sure the above are all excellent IWB/OWB holsters they aren't for everyone. I have some nice IWB leather gear that I wear very seldom, it doesn't work for me in most cases. The M&P compacts give you a wide range of options, for me the answer is a Galco Ankle Lite ankle holster for my M&P40c. It is a very concealable package being not much larger than a J-frame 38. Weight is within 2 ozs. of a steel J-frame. All in all it is a perfect fit for me.
Cheers,
Sam