The key to buying a gun is finding one that fits comfortably in your hand. That makes control-ability a lot easier. Next is to shoot that model in all available calibers. While it is true that most law enforcement agencies are now using the .40 round, it is, as someone had mentioned, quite a snappy round. I'm a big guy and normally shoot about 1000 rounds a week. I find that I can comfortably shoot .45 ACP all day long but can only shoot a limited amount of .40 as it does have a lot of snap to it causing some pain in my old, aging hand and arm.
May the Schwartz Be With You.