Buy both, then buy other calibers, then buy a bunch of ammo for every gun you own, its only money, and they this gov't is spending it, it wont be worth much anyway in the future! having said that, get a 40, if you can ONLY handle the recoil of a 9mm and not a .40 S&W then there is prolly some other issue with that person. its not really that much of an issue as other people have said. .40, bigger bullet, great speed, very accurate, glock 23 is a great weapon. Some people argue about cost, the reality is that you are going to spend money on guns, so buy what you want, and are you shooting thousands of rounds a year? most arent. Dont worry though, if you are like most people, you will buy more than just one gun its fun to have lots of different toys.