.45 Auto has more lead, and there's lots of fans of the .45 semi-auto cals, especially .45 ACP.

40 S&W is a good round, and it shoots well, makes a nice sub-compact. My dad has one. I think you'll be happy with either one, and yes, the .40, with home defense loads, has PLENTY of knockdown power for home defense, so no one is going to sue you after getting hit with a personal-defense load, because they'll be dead.

Stay away from the Taurus Millenium, the trigger pull is bad and can't be adjusted.