You will see better results faster with a semi-automatic handgun. Revolvers pose some interesting carry problems. Carrying spare ammunition securely, yet concealed, can be a challenge. Shooting small revolvers accurately can be a serious challenge.
As mentioned previously, go to the range and rent different guns. Fire at least 100 rounds through each gun you rent. However, it is far more important that you get some training prior to purchase. I recommend you buy a few private range lessons and then attend a two day defensive pistol class using a rented gun. You will learn quite a bit in those two days. You'll have an idea regarding the attributes you find desirable and undesirable in a handgun. Your father may come to a slightly different conclusion.
9x19mm and 45 ACP are great starting cartridges. Both are adequate for self-defense and can be used for action pistol shooting. 45 ACP is easier to reload, but commercial 9x19mm ammunition is far more economically priced. Furthermore, there is a much wider range in gun size for guns chambered in 9x19mm. Even the smallest handgun in 45 ACP will be much larger than a Kahr PM9.
If after this you have no idea what to buy, just get a Glock 19. They're highly reliable and accurate enough for most uses. If you decide you dislike it, you can always sell it for approximately what you spent.
If you have to get a revolver, then buy one with a 4" or longer barrel. A 4" barrel is still compact enough to more easily manage concealed. I very much dislike S&W's current offerings due to some problems in build quality (inspect carefully before you buy and use the "Revolver Checkout" document available on this forum). I prefer either the Ruger GP100 or the Ruger SP101. Both are reliable, accurate, and easy to work on. S&W has much more variety, but you'll have to put up with cruddy MIM parts, THE LOCK, two piece barrels (in many models) and so forth.
Last edited by tomrkba; December 15, 2012 at 06:31 PM.