Go with the 23... hell I went with it twice... I have two of them.
Yes, the .40 has more recoil, but that is because it has much more power and stopping effect.
Dealing with the recoil is something that practice can over come. The recoil honestly isn't bad at all.... I can let off a string of 3 double taps, with about a second between them, and land all 6 rounds in a 3" group in the center of mass of a target at 15 yards. Practice makes perfect... the more you train with your weapon the more effective you will be with it.
Plus, if you go with the .40, you will be less likely to need follow up shots anyways do to the power it delivers... the 9mm you would (unless it was in the head).
Glock 19: 15 9mm
Glock 23: 13 .40 S&W
(However, you can add a plus 2 mag extension to your mag, and even this out,
or you could just use Glock 22 mags which hold 15 but will stick out the bottom)
For a review of the best .40 round to use, click
here