if you dont reload the best calibers that are abundant and are rather cheap in price compared to other calibers are 9mm and 40s&w I would recommend either a glock, Springfield XD or a Taurus Millenium Pro in either of those calibers. If you reload or money isnt a problem than go with a 45 acp in a springfield or kimber 1911 i feel those are the two best in the market or if you prefer light weight polymer frame guns then go with a glock or a Taurus millenium pro. IMO 45 acp is the best choice for self defense.