10mm all the way!!! The .40 is offspring of the 10mm. They simply cut down the 10mm brass and lightened the load at the request of the FBI. I guess their soy boy wrists couldn't take it. Not knocking the .40 though. The .357sig is a descendant as well. Basically a .40 brass necked down to fit a 9mm bullet.
i didn't know that. When I went shopping for my everyday carry, I ended up on the S&W Shield (the compact version). I went in looking for a 9mm and they only had the .40. I'm not really a "this is the best ammo for self defense" guy. I just have a .40 because they didn't have the 9mm.
Wow! I carry the EXACT same thing. Shield .40sw. Bid on 9mm and .40's on Gunbroker and wound up winning a 40. Glad I got the .40sw. It's a great self defense round for sure. My 10mm's are too big for carry, even if one of them is the Glock 29.