IMO the .40 S&W is the better self defense round. I use a Glock 27(40 S&W) as myoff dutygun. The 9mm would be cheaper to shoot though and could add upif you shoot a lot. One thing to keep in mind. If you buy a Glock 27, 23 or 22(all .40's) you can buy 9mm conversion barrels for them and you can also buy .357 Sig barrels.These barrels run about $100 from Lone Wolf distributors.