Don't worry about round counts. All of these guns will last longer than you with some very basic maintenance (a spring here or there every 5,000 rounds).
I have experience with the Glock, PX4, and M&P. I would probably take the PX4 because they shoot great and I prefer hammer-fired guns. Tunnelrat is correct, you still haven't figured out whether you want a striker gun or a DA/SA. Do some Googling and find the difference between them, then decide.
I second the recommendation to add a Sig Sp2022 to your list, and also the Walther PPQ.