I have a small collection of 9mm Glocks. My 19 is a Gen. 3, so I get brass to the face a lot more than I'd like. On the good side though, the 19 functions perfectly with the 33 round magazines, and of course, with the 17's.
I thought it would be my CCW gun, but I'm too fat to fit it IWB. That led to getting a Gen.4 26. Then I decided that I don't need to carry all the time anyway.
If I were doing it again, I would NOT have 5 of the 15 round mags for the 19, as I do. Better to use the 17's as spares, and carry a 15 in the gun because it fits better for carry.
As for ballistic advantages of 9 vs. .45, due diligence is in order. Check this story for one cop who found that shot placement is the whole game:
http://www.policeone.com/police-heroes/articles/6199620-Why-one-cop-carries-145-rounds-of-ammo-on-the-job/
His opponent was hit 14 times with .45 cop ammo before he gave up the ghost. The cop was on his very last mag of .45, having started with 47 rounds. Now, he carries 145 rounds of 9mm.
I shoot only hand loads in my Glocks. My defensive load clocks 1,400 fps in the 17L, and drops to 1,250 in the 19, with a 124 gr. JHP. That's still heap big medicine.