Yes, 5.56x45mm NATO remains the most popular caliber option for AR15 pistols.
There are some downsides to 5.56. You won’t have the same range or terminal ballistics as a full-size rifle, since 5.56 ball ammo relies on ball ammo, but a quality 77gr bullet can make up for much of the performance loss. AR pistols will also be much louder and gassier than rifles, and the recoil impulse may be very slightly larger.
However, these are all marginal trade-offs compared to the handling advantage of a short barrel. If you’re shooting from a vehicle or a tight hallway, AR pistols will be substantially more effective than a full-size rifle. Your AR pistol will also be somewhat lighter, and the balance will make it easy to carry and shoot on the move.
If you stick to a 10.5-inch or longer barrel with quality defensive ammunition, an AR pistol can achieve terminal ballistics comparable or superior to a full-size rifle with standard XM193. You’ll have an effective range to 300 yards, which is plenty for almost any domestic purpose.