Doc, you pretty much nailed it right there.
The two rounds are similar enough that it often just comes down to personal preference and which one you shoot better. Some people prefer the .40; me, I prefer the 9mm.
Though, if you're on the fence about which one to get, you might want to consider the cost of ammo. If you're like me and you don't have much extra money, you like to shoot a lot, you live in a tiny apartment where the wife won't allow any reloading equipment, then the 9mm comes out on top due to the significantly cheaper cost of ammo.
0331: "Accuracy by volume."