G27 -perfect all around Glock if can only buy one. Interchangable with larger mags to shoot like a full size gun; easily concelable under most conditions without looking like a slob with your shirt tail out; perfect self defense caliber(per FBI) but easily converted to 9mm if you want to practice cheap or .357sig if you desire. I would say G26, but you are stuck with 9mm no options G19 and 23 are slightly large for year round CC unless you want to have consistant shirt out look.