Many people decide they want or need a gun and only have the budget to purchase one gun.  There are a lot of choices out there, so how does someone choose their one and only gun?  Most people will ask friends who have guns, others will go into a retail store and be "sold" a gun.  The smart people will read articles like this which give you good insight on choosing one.

The first thing to figure out is a budget. How much are you willing to spend on a gun that could potential save your life?  Now that doesn't mean you need to go out and buy the most expensive gun because you value your life.  Most gun owners never have to use their weapons for self defense.  I never have, and hopefully never will.  The point I'm trying to make is not to buy the cheapest gun, but don't go overboard either.  You don't need the $900 H&K when the $600 Glock will do the same thing.  High end guns are bought by gun enthusiasts and collectors.

Miltary and police both use mid-level priced guns: Glocks and Berettas.  The simplicity and reliability make Glocks are great choice.  Nearly every gun dealer carries them, they are easy to shoot, and easy to clean.  Here is are some things you should consider:

1. Size (model)
2. Caliber

Glock makes several of various size.  Full size, compact, and sub-compact.  The sub-compact are the smallest of the models and may not be easy to shoot for those with small hands.  You can find more information about Glock models here.

The Smith & Wesson M&P is also a great choice for single firearm. Hand guns from Ruger are often overlooked as good choices but are solid firearms. Springfield XD models are very similar to Glocks are have gained a cult-following among concealed carry owners. Purpose-built concealed guns like the Ruger LCP is a terrble choice. It's too small to shoot comfortably and is very hard to shoot accurately past 10 yards. It shoots a .380 caliber which is a somewhat smaller version of a 9mm but still fairly expensive in retrospect.

I always suggest 9mm because it's an effective self-defense caliber. Also, it's much cheaper to shoot than .40 or .45 calibers.  If you can only buy one gun, a Glock 19 is my personal favorite.  It's a good size that shoot well, yet still small enough carry concealed if it's possible to obtain a carry permit in your state.