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Like said above, the gun you shoot the best is the best gun for you. All of the guns you named are medium priced guns with good name recognition. This is like asking which is better: Ford, Chevy, Dodge, Honda or Toyota.
I have shot the Beretta Storm Compact and the PPS both in .40 caliber. I have shot a SR9C but not a .40 caliber and I have shot the standard M&P in .40 but not the shield
I personally loved the Storm. I really liked the SR9C and assume the .40 would be nice. I really liked the standard M&P but have never shot the Shield. I have shot the .40 PPS and hated it. I would never own or even borrow a PPS but you see above that Vincent says he shoots his very well and loves it. That doesn't make me right and Vincent wrong or make him right and me wrong. It just means he and I have had different experiences with a PPS and/or have different tastes in guns. I loved the Storm Compact. He might hate that gun.
If there was one all around "Perfect Gun" there would only be a need for one gun on the market. If you can, try renting or borrowing all 4 and see what you like. I have a friend borrowing two of my guns, borrowing another from another friend and going to rent two at the range today so he can shoot all 5 the same day and decide based on his experience.
Myself, I REALLY like my PPS in 9mm---personally, I have found that the smaller pistols just seem to work better in 9mm than .40---ammos cheaper too...
I have a full size px4 storm and its a great gun. My first and only ccw gun I just got is the walther pps 9mm and its a sweet little shooter.
Good luck...