Fist off as stated previously you have to decide what you are going to use the firearm for (Home defense, Personal carry defense, Target shooting) then you have to decide on a round to use .380 (BUG) 9mm, .40, .45 are very common to carry, I personally love my 9SC, had a Glock did'nt care for it much also have had Ruger's and S&W's semi-autos are usually the way to go as reloading is much quicker and capacity is higher.
My suggestion would be to go to a local gun shop/range and rent a couple of diffrent calibers and makes and make your decision or hook up with some people you know and shoot theres if that is a option.
Remember unless you compete or target shoot what a hand gun is for and what distance it's meant for