Stick with 9mm; ammo is cheaper than the alternatives and can be very effective if the right bullet is chosen.
The average Glock is FAR more accurate than the average shooter, so putting rounds on target is not a function of the gun, but the person. Yes - I do understand that the relationship between person and pistol is important; I would not disagree. But most decent brand guns are more than accurate enough for any reasonable task you'd put to it. When folks don't shoot well, it's most often not the gun, but the person (poor technique, poor hand fit, etc).
That being said, get the little model 26. It is one of the more versatile guns out there in it's class. Can easily shoot very well at 25 yards (few folks would EVER have to shoot that far in a self-defense situation). Very concealable. And since you already have the full size model 17, then your mags will interchange with the 26! If CC and home defense are your aim (pardon the intended pun), then the 26 will fill the bill nicely.