It really comes down to what you expect the gun to do? What is its primary role? A daily carry and primary defense gun? Or a "do it all gun, target, safe, carry, defense...etc"....
Primarily a defensive gun...go for the 40....It has more knock down energy and is generally a more potent caliber for that purpose. Ammo is on the spendy side, but for its purpose..who cares. This is if you have other guns to "play" with....a .40 isnt my first choice as an "only gun".
For the do it all gun or if its an only gun...easy choice 9mm...almost the energy of the 40..not quite, yet ammo
is literally 1/2 as much and is very very common.
Thats my take on it......
Oh ya, the 40 has porting which may produce more flash at night if used in a defensive situation. But its also going to reduce recoil for a quicker follow up shot.....
Shoot well
