I ended up buying both. With good self defense loads I don't really feel much of a difference in recoil. With Wally World practice ammo the 9mm (G26) is a soft shooter but the .40 (G27) still feels close to the recoil of the self defense loads. While I like the G27, I would recommend the G26 over it even though my other Glocks are not in 9mm.
Really you should try to go shoot both with self defense ammo and bulk ammo and make your choice from your experience.