depending on dept, .40 caliber is the way... M&P is an excellent choice, my agency issued glock 23. I like the M&P and personally think its a much better weapon than the glock, fit, feel, recoil, grouping. I carried the glock for years and had no problems, it was'nt my choice of side arm. So now that I am retired I went to a better choice for me. the best advice i can offer is one that you will see all over the forums, go to your LGS/Range, put several choices in your hand, shoot the ones you like if they have rentals available. Then you pick what is right for you. There are not many agency's to my knowledge that still use the 9mm, most have made the switch to the .40, i don't know of any that use the .45. In my opinion .40 is a great round, knock down + capacity. Good Luck in the academy be smart stray safe, best tool you carry as a LEO is your brain, use it.