Google Dr. Martin Fackler
In a defensive use, you need sufficent penetration and wounding abilities. Without a long, drawn out discussion, I believe the minimum penetration you want is 15+ inches to hit something vital, and you want good expansion in hollowpoints to help hit something vital. (I am at work so I can't get to alot of the specifics).
Also, each gun shoots better with different loads. More accuracy, better feeding, less muzzle flash, etc. Try a few different loads and see what you like.
I don't have a .40 so I can't say specifically, but I like big bullets with good expansion that feed very reliably. I use Speer 230gr GoldDot HP in my .45.