Personally, I don't care much about the difference between 9 and 40. If you shoot one better than the other, stick with that one. For example, my wife prefers to shoot a 9 so I also go with a 9 for ammo compatibility and in case she grabs mine. Same gun, pick what you like and learn to use it VERY well.
I don't feel undergunned with a G19 and a spare mag.
Of course, all of that goes out the window if you want to buy the G32 / 23 combo I'm selling
