Hey!, handgun talk! COOL!

For hunting deer, I like my S+W 629 .44Mag revolver.
I got the 6" barrel since it doubles as a "bear defense" gun when I visit my uncle's place in the north woods of Wisconsin. He has a cabin in the middle of nowhere and it's a bit of a walk to the outhouse. It handles quicker than the longer barrels, and I don't lose too much velocity to be effective hunting.

If you want a handgun for defense, there are two schools of thought: Big/Slow bullets vs. Small/Fast. Both can be effective, but each has their strengths and flaws.
You will also have to decide between revolver and semi-auto. Also you have to select a type of action. Pick from single-action, traditional-double-action, or double-action-only.
Single-action has a nice clean, short trigger pull, but needs to be cocked before firing or kept "cocked and locked with the safety on.
Double-action is where the gun can be kept with the hammer down. When the trigger is pulled, the hammer is both cocked AND released. Semi-autos that have this action type cock the hammer every time after the first shot. You may also manually cock the hammer for your first shot if you are so inclined.
Double-action-only guns do not allow for the hammer to be cocked before a shot. The hammer is only cocked as part of the trigger stroke, giving you the same consistant pull every time. Striker-fired pistols, like Glock, Kahr, and a few others, are operated the same way as a double-action-only, but the internal mechanics is a bit different.

Good defence calibers for revolvers are .38special, .357mag, .41mag, .44 special. You can use .44mag too, but it tends to over-penetrate.
Don't go any smaller than a .38. It would take very good bullet placement to stop someone, and you never know when you would get a chance for a second shot.
If you like semi-autos, 9mm 115g can be OK if you load it very HOT.
The old .45 is hard to beat(230g loads unless you're shooting from a very short barrel, then go lighter like 165g). Glock makes a great 13-round .45 (model 21) which I highly recommend. Reliability is fantastic. It will eat anything you feed it and come back for more. although I have never owned a Sig, I hear their reliability is similiar.
A good fast round is the .357sig and a nice balanced in-between load is the .40. I Like it in 155g and it is a big favorite with law enforcement. Doesn't over-penetrate and will still go through windshields nicely.
The Border Partol uses the .40 155g, and they have done extensive testing and comparisons with others. Terminal ballistics is very important to them bacause they are on the top of the list when it comes to the raw number of officer-involved shootouts per year. They know what works and what doesn't.

The 9mm was much more popular before the hi-capacity gun ban, and before the FBI's Miami fiasco where multiple hits from 9mm failed to stop 2 criminals. The lack of effectiveness cost several agents their lives. The FBI has since switched calibers.
People who carry concealed weapons can be tempted to choose a .380 or a .25 because the guns are very small. These are considered pretty feeble rounds and are not recommended unless you REALLY have no way to conceal anything bigger. I would recommend a HOT loaded 9mm 115g before either of these. There are some nice 9's out there that are almost a small as a .380.

If you just want a fun plinking gun or a historic piece, I will turn this over to other members, but if you want to talk more about defense guns, e-mail me or we can talk more here. I have done a fair amount of research on defense calibers and handguns for them.

-Bulzeye

Keep 'em all in the Bull.