Get the 9mm. You'll shoot it more because 9mm is cheaper than .40, it has less recoil so it's easier to manage, and you gain a couple of more rounds with 9mm over the same sized gun in .40. For your first gun, if you're planning on carrying, the 19 will be a bit easier to carry than the 17, but you still carry 17 mags as your backup mags since they fit in the 19. Also, don't spend a bunch of money trying to improve the trigger or any other after market parts. You'll be better off spending that money on ammo or training. The only after market thing I'd buy is a set of night sights for it. Get the 9mm and don't look back.