Have a 27 and carry it on occasion (typical carry gun is a 23). Nevertheless, I would recommend a 26 for the reason that it has slightly less recoil and will therefore be slightly easier to shoot rapidly in a self defense situation. I'm stuck in the 90s with my .40 self defense guns.
Were I to start over, I would get 9mm exclusively, but I'm too heavily invested in .40 (ammo, reloading components, magazines, etc.) to switch now.
Glock and M&P Armorer
NRA Pistol Instructor
Illinois Concealed Carry Instructor
Glocks: 17, 17L, 22, 22C, 23, 24C, 27, 34