9mm has cheaper ammo and will hold more ammo. 40 has more power but is a good in between of the 9 and 45. You can recover faster after each shot vs the 45. Get onto u tube and watch ballistics in jell, its pretty cool to watch

You could always get a g27 and buy the 40-9 conversion barrel. They are both the same size frame.

I carry a 19 now, so if I only have these 2 to choose from, it would be the 26. I have no experience with 40 calibre.

I carry a model 22 as a carry gun, I have also found a great carry system iwb look into versa-carry

Shoot the largest caliber you comfortably can. So if not .45 then IMO go with the .40. The market is flooded with accessories for glock 9 &40.

9mm ammo is cheaper. I have the 27 because I like the extra odor the .40. your mileage may vary and either is good.