Why are you wanting to buy one? Is it for home defense, carry, competative shooting events, vehicle carry or just to have one? If you just want a gun it won't matter what you get, you will have a gun.

If you want something for everyday carry you need to purchase a weapon that you are comfortable with on your person in the winter as well as the summer. If you want something for the home you want to make sure you don't have a firearm that will penetrate multiple walls. The load that you shoot will affect this as well.

There is a lot more to think about before you just go and buy a gun. Go to the range rent multiple guns you are interested in. Do your research on the benefits of a .40 s&w over a 9mm or a Glock vs. a Springfield.