I vote for the 9mm..
Cheaper ammo, one more round in the mag, less recoil, etc.
But I've never cared for the 40cal in any handgun...YMMV
I like 45ACP as well, just can't afford to keep it around..
Really liked my XD9sc, had it hard chromed, but still ended up selling it.
The 9mm Sig P239 won on the carry pistol.
Two years later my 3 inch 9mm 1911 is now the choice of carry gun.
Yep, I'm pretty big on 9mms..

You find a lot of info stating modern day 9mm rounds are quite effective.
But shot placement in any caliber is the most important thing.
Good luck..