Now that I have come out of the closet:
I own all three but prefer the Model 23 over the Model 19 because of the caliber (.40 verus 9mm).
I find the mid-size better balanced than the Model 17/22.
I CCW a Model 27 as I seen to shoot better than the Model 26/19/23.
The first Glock I saw/handled was a Model 21 in 1990. I was totally impressived by a 13 shot .45acp with night sights service weapon. I was carrying a six shot .45acp revolver at the time.
Jimmy