Best caliber handgun for home defense?
If you are asking what is the best caliber for stopping intruders the list includes .45, .357 and 10mm.
These are a few calibers that most folks agree with as being "man-stoppers"
Again to generalize, most folks agree that the one-shot-stopping abilities of the 9mm, .380, .38 are questionable (not looking to start something) For that reason, I do not believe they are the best calibers for HD.
If you are primarily concerned with stopping potential human intruders, I do not agree with the questionable calibers listed here unless ITS ALL YOU CAN HANDLE ACCURATELY. If you own .45ACPs and are comfortable with them, STICK WITH THEM. They fire a relatively slow moving slug. Velocity plays more of a part in penetration of hard targets than mass does, IMO. If collateral damage (wife, kids, neighbors, pets) are a big issue (apartment, urban environment) you should be grabbing a shotgun with large diameter bird-shot (2s are my choice), and not a handgun.
If you still need to use a handgun in apartment or similar, frangible slugs might seem like a good idea, but again, highly questionable. Also VERY expensive to function test in a HD semi-auto pistol.
The largest flaw discussed about safety slugs or frangible ammo is their inability to penetrated heavy clothing. If you live in a warm climate area, or for summer use, and you've function tested, they can work.
Ive fired the glaser blue tip safety slugs into wet books, the damage is INCREDIBLE. When they expand, they are like a tiny grenade opening up with bits of metal fragments. I fired them in .357 and .223. In both calibers the glaser slugs did not penetrate as deeply as HP ammo, but not much less (2-4"). Check out link:
http://thefiringline.com/forums/showthread.php?p=4546227#post4546227
Shows photo of glaser impact