What would be the best caliber for a self/home defense handgun
Since we are talking only "handguns" here, I would say the largest caliber that you can shoot well without any undue problems. Revolvers are handguns as well and 357 Mag takes care of almost any problem that you will run into, however the recoil on that round is stout and most revolvers are limited to 5, 6 or 7 rounds. In most cases that would not be a problem, since I believe that one or two rounds would be all that you would use against a single attacker. If however, you feel that the recoil is too stout or that your situation would require more shots against many attackers then the 9mm will give you the most number of rounds per magazine. While I am not a fan of the 9mm for home defense (I do own 2 and use them), I would say the 45 ACP would be more approprate at stopping an attacker, but then again you are limited to the number of rounds that the pistol will hold (7+1). The comprimise of a 40 S&W that holds 12, 13, or 14 rounds might give you the edge, but from my experience with it the recoil is substantualy less controlable than either the 9mm or the 45 ACP.
Each caliber has it's benefits and draw-backs and must be weighed on the basis of the owner's needs. Only you can determine what will suite YOU BEST.