First, you need to find a pistol that fits your hand. Yes, some will fit better than others. Between the Sig, Berette, Glock, 1911 (multiple brands make the 1911), S&W, Taurus, and Ruger brands, find you or 2 that you like and do some research on that pistol. My personal favorite is the Sig 226 family of pistols. I carry one while on patrol, in 9mm. It fits me like a glove, is highly reliable, simple to use and maintain, and damned accurate. There has yet to be another deputy that can put more rounds on the paper as fast and as accurate as I that shoots of .40SW. Most of them are shooting the Glock 22 (.40SW).
If you are new to handguns, I highly suggest the 9mm Luger for a caliber. Why? With the low recoil you're less apt to develop bad habits. Trust me. I've taught many people how to shoot and the larger calibers (.40SW, 357Sig, 45ACP, etc) produce more recoil than anything else. With the modern day performance ammunition available, the differences between the wound channels in minimal, if any. Accuracy is key and is the most paramount item. No sense if using a sledgehammer to drive a stake into the ground if you cant hit the stake. A 5lb hammer will do just fine. I carry a Sig 226 in 9mm while on patrol. There has yet to be another deputy that can put more rounds on the paper as fast and as accurate as I can that shoots of .40SW. Most of them are shooting the Glock 22 (.40SW).
You can buy a police trade in Beretta, Sig, or Glock for a very reasonable price. Do a search.
One last thing: there is no "best". Only what works best for you. Dont listen to the crowd that says "X gun suxors". There are reputable brands and not so reputable brands. The brands I mentioned above are the most common and all are reputable. The following, IMO, are not so reputable and I advise to stay away from the Lorcin, Phoenix Arms, and other such cheap $50 handguns. They truly are made cheap.