The first thing you need to look at is the law where you live.
If your state is one of the ones with restrictions on magazine capacity, or on the rifles themselves, If your state does, then getting a semi auto PCC may be a moot point.
If that's not an issue, other things to look at are, what kind of thing are you looking for? A military STYLE carbine? One that is more "civilian" looking? A semi auto reproduction of an SMG?? A purpose designed PCC, or an adaptation of a different gun (such as the AR) to make it a PCC?? These are things to consider.
The intent of a pistol caliber carbine is to extend the easily usable range over what is possible using the same round fired from a handgun. The carbine has "more to hold on to" greater sight radius (iron sights) often allows optical sights, and the longer barrel gives a boost in velocity reducing drop at longer ranges. Easier to use (aim and hit accurately) at greater distances than the handgun.
I've had a couple, purpose built guns, not adaptations of larger actions to shoot pistol cartridges.
One was an Auto Ordnance M1927A1 Deluxe. Fun gun, really neat, literally a semi auto legal Tommygun. .45ACP. Heavy as hell (over 10lbs). Mine worked well (not all do, apparently) and very accurate once you mastered the spongy mush that was the trigger pull. Not practical, but lots of fun.
The other is a Calico 9mm carbine. Purpose built, unique design, some great design features, pretty light, accurate, trigger is on the stiff side but usable, and uses 50 or 100 rnd magazines.
I would choose it over any AR (unless you are going to use the AR as a multi caliber platform). I don't know if they are still in production though. Thanks to a majority of misguided morons in my state, I can no longer buy the magazines, and if the pending bill becomes law won't be able to buy the gun, either. I get to keep what I've got, though, how kind of them,.....
The Kel-Tecs are lower cost, not very stylish, but from what I've heard, they work, and if not, Kel-Tec fixes them. I have no direct personal experience with them, though.
Semi auto PCCs are high on the gun banner's hit list. Personally, I find lever gun PCC to have more practical utility in my life, good companions to my revolvers, and better performers in the game fields or pest control over the usual semi auto pistol cartridges.