I am looking to purchase a 9mm CCW compact semi-auto. For various reasons, I have narrowed my search to the Smith & Wesson M&P series compact or the Beretta PX4 Storm sub-compact. Does anyone here have any useful input for me? Please keep responses polite...

Uber
I don't have experience with the M&P, but I do own a full size PX4 9mm. It shoots flawlessly and is more accurate than I am. The only thing I would say about the PX4SC is that Beretta delayed about 2 years from announcing it until they finally started delivering it this summer. They had several false start delivery dates along the way. The full size PX4 has a rotating barrel, the PX4SC has a tilt barrel - don't know how that will play out over time, but the mechanisms are different. Many other semi-autos use the tilt barrel, so that is not a new concept. You might want to see how the first deliveries perform to see if there are any bugs that appear. As you know there are often things that don't crop up until the public gets their hands on the new design. On the positive side of the PX4SC:
1. It has a safety/decocker (which I recommend) - which I wanted.
2. It has an exposed hammer - so you can fire SA/DA - which I wanted
3. It has exchangeable grip inserts to suit your hand size - which I wanted
4. It is quality built and easy to maintain - which I wanted
Personally, I waited quite a while to buy a PX4SC and finally gave up and bought a H&K P2000SK 9mm. What a sweet gun!!! It is out of the price range of the M&P & PX4SC, but if you can find a used one I would highly recommend checking it out.