Since you are trying to select between two similar Glocks it is a question of ammo not weapon.
The .40 (M23) will be the way to go for CCW/LEO carry as long as you can handle shooting something larger than the 9mm. I have two M23s (one issue, one personal) and its a great firearm for these uses. Using the military example to select a defensive round is poor logic as the selection criteria for a general issue handgun round for the military is much different than that used for CCW/LEO purposes. Hense the movement away from 9mm towards the .40 S&W in the LEO community and even the military special ops folks have rejected the 9mm.
Go for the 9mm (M19) if you have trouble shooting the heavier round or if your interest is more towards punching paper.
However, if you decide you should go with the 9mm and will use it for a CCW. I would reject a Glock completely and instead go for a Kahr MK9 which would put the concealed back in CCW.
The .40 (M23) will be the way to go for CCW/LEO carry as long as you can handle shooting something larger than the 9mm. I have two M23s (one issue, one personal) and its a great firearm for these uses. Using the military example to select a defensive round is poor logic as the selection criteria for a general issue handgun round for the military is much different than that used for CCW/LEO purposes. Hense the movement away from 9mm towards the .40 S&W in the LEO community and even the military special ops folks have rejected the 9mm.
Go for the 9mm (M19) if you have trouble shooting the heavier round or if your interest is more towards punching paper.
However, if you decide you should go with the 9mm and will use it for a CCW. I would reject a Glock completely and instead go for a Kahr MK9 which would put the concealed back in CCW.