The midsized Glock 19 (9mm) and 23 (40) are VERY popular for carry.
Great mag capacity for the size, no featuresthat will snag during a draw,no sharp edges to ruin your clothes, factory installed night sights, a light rail, easy take down for cleaning, a great finish that resists corrosion well, and a TON of high capacity mags on the market at low prices.

You can also pack a higher capacity mag for the full sized gun (G17 or G22)as backup. The G26 and G27 (ultra tiny subcompacts) are also popular, but the grip is too small for me unless I use an extender. Since I have to do that, I might as well keep the longer sight radius (and greater margin of error for aiming) and longer barrel for a slight increase in velocity anyway. The baby Glocks can be tough to reload without some serious practice since your bottom finger wiil almost alwayshang in the way of the magwell. The grip angle is also different in the baby Glocks vs the oneyou will findfor mid and full-size models.

If you like the feel of the grip and the way the trigger works, it'd be hard to find a better choice, even used. I bought a used Glock 21 for the house about 8 years ago (full sized 45), threw some Tritium on top, practiced my wallet dry every week, and found it to be very accurate, and extremely reliable. It's just too big for me to carry.

Every time I go to the range, that G21 is the first and last to blow smoke.