I've had two PWS, a mk 111 mod 1 and mk116 mod 2, and I have an APC223 12".
The PWS is a great system. The gas settings are fantastic, their long stroke has some benefits over other types of AR pistons, and overall I was very happy with them. I sold them both two throw more money at other stuff but I do miss the mod1. I run my stuff almost exclusively on LMT MARS lowers and it made a great setup. It's a propretary system, but when I emailed PWS, I was able to purchase a spare complete BCG for like $120 during peak covid panic. Use any AR style bolt, firing pin, cam pin you want. Biggest complaints:
1. Semi-Proprietary system (as most AR pistons are) but seemed as though I could get spare parts when I wanted them for a good price. The other bits are AR compatible so not a big deal.
2. The holes in the gas valve for adjustments weren't large enough to stick an m193 bullet tip into for leverage. I had to use the tool they provided after it started to get hot or stick with carbon to make adjustments.
3. Gas valve was pretty hard to remove after enough suppressed usage. I bent the supplied tool. Best bet is to pound it with a wooden dowel from inside the gas tube, or at least thats what I'd try if I still had it.
The APC223 is very, very smooth. The adjustable gas works great and the differences between the two settings is substantial enough to give you two options that don't feel like they are too similar. The gas adjustment is also easier to accomplish o nthe fly than the PWS becasue it's exposed. Being two position with 90 degree throw, its obvious what gas position you're currently in at just a glance. My biggest complaints about the APC:
1. It's very expensive.
2. Its a complete proprietary system and spare parts aren't always available.
3. The ambi bolt realease is hard to reach with my finger without breaking grip.
4. The forend isn't as sleek, comfortable, or easy to configure accessories as an AR style rifle.
5. Not all brands of QD mounts work with the top rail of the APC. Midwest Industries do, and they are generally my favorite.
6. I found sling mounting to be a bit more of a challenge, but I have the reciprocating charging handle version which played into that. The Pro upper will be better in that regard.
7. Depending on optic choice, charging handle can be a knuckle-buster on your optics mounts
Conclusion, both are functionally awesome. The PWS is easier to justify price wise and sustainability wise. The APC feels more exlusive if you're into that feeling and their machining is second to none. Both have been 100% reliable for me suppressed and unsuppressed. If you have an specific questions, I'll try to answer them for you.