The .380 is more powerful and less accurate. The .32 is almost pleasant to shoot, the .380 hurts. With the .380, it is necessary to dremel the face of the trigger and the inside of the trigger guard and make it very smooth. When you fire it, your trigger finger slams into the front of the trigger guard. If you are going to shoot more than two or three magazines, put a band aid on your trigger finger first, it will get bloody. That said, it is generally my every day carry. Good .380 rounds are in the same power range as .38 special, but in a very compact package. I use .380 Remington golden sabre ammo. In the .32, I use either Winchester Silvertips, or the much more powerful Fiocchi hollow points. I prefer the Fiocchi. The Fiocchi .32 hollow points have the following velocity and energy values in the Kel-tec. 1071 ft/sec and 152 ft/lbs energy.
I don't have data for the .380.
The Kahr PM-9 with Winchester Ranger +P+ ammo yields 1131/360
.38 special semi-wadcutters are on the order of 771/208
Really hot .380 ammo can be on the order of 1050/220. This is from an internet search and is probably from a longer barrel than the Kel-Tec. The other values are chronograph measurements from my own guns.
All of these little pocket autos really need to have the feed ramp polished and about 200 rounds through them before they can be considered reliable. Kel-tec has fantastic customer support. Kahr seems good too. S&W revolvers benefit highly from a slight lighter weight trigger rebound spring. It is best to leave the hammer spring alone, if used for self defense.