If I were to venture a guess, I'd say they are about #4 on the popular list, behind the 19, 17, and 22.
The 19 and 23 frames are identical and the slide is nearly so. I started to buy a 23, but .40s&w ammo is stupid expensive for what it is when compared to 9mm and 45 acp. So I got the 19 so I could have some cheap plinking.
Life is hard; it's harder if you're stupid.