The 23, being mid-sized, can be concealed better and still is a full sized duty pistol. Having 14 rounds of .40 (or .357 Sig if you get a Glock OEM .357 Sig barrel) is pleny of both power and firepower. Plus the FBI is happy with it.
Yes the 19 is a great gun to, but a 23 will allow you to have 4 in one guns. .40, .357 Sig, 9mm (with Lone-wolf 9mm barrel), and .22 (with AACK .22 unit.)