Instead of worrying about sub-compact vs compact, ask yourself why you aren't considering a full size?
Clint Smith's words:
"A full size pistol is big to carry sometimes, but it is always big in a fight, and big is what you want. You never hear anyone complaining that their gun was too big in a gunfight."
An example: If you consider purchasing a Glock Model 19 for your carry piece, why don't you consider a Glock Model 17. The size of the 17 is not much bigger than the 19, and you have the insurance of added ammo capacity, and a slightly longer barrel, which will enhance the effective range of the fight you can bring.
Another example would be to look into the world of the revolver for defense. There are many choices out there, and you can choose from having a capacity of 5, 6, 7, or 8 rounds (.357 Magnum is popular with the different capacity offerings) at your disposal at a time. I recently shot a 7-round Smith and Wesson revolver that was smooth as butter, and very accurate all the way out to 25 yards and beyond. Revolvers are overlooked too much in this day and age. You cannot beat the simplicity of the design, and the reliability.
If you want a sure thing in the semi-auto world, though, I have only 4 numbers for you to remember........
"TRAIN WITH WHAT YOU HAVE, NOT WITH WHAT YOU WISH YOU HAVE."