Newer is better in this case
I have owned the WALTHER PP and PPK, both in .32ACP. I also own two SIG 232 in .380ACP. I liked the SIG 232 blue model (aluminum frame) so much, I bought a second.
I consider the SIG 232 superior to the WALTHER PP for several reasons. The SIG has an aluminum frame that saves several ounces in weight. The SIG has much better sights, especially if you get the tritium night sights, a real bonus for a defensive pistol.
The SIG also has a MUCH, MUCH BETTER GRIP and the SIG trigger is in a different class from the WALTHER, noticeably smoother. The plastic, non fingergrip stocks on the blue, aluminum framed SIG 232 are about perfect for me, ergonomically, as I have average size hands. They fit perfectly, recoil is mild and control great.
The SIG has two other improvements over the WALTHER PP. First the SIG DE-COCKER works just like the larger framed SIG pistols and is the best DE-COCKER ever made, in my experience. It is fast and safe and when used, it does not put your pistol into a NON-FIRING MODE which you may forget to switch off.
The WALTHER PP safety works fine, but if it were a de-cocker like the BERETTA G series of pistols, I would like it more.
The other advantage is the take-down procedure could not be simpler. Just flip down the lever and let the slide forward.
In shooting, I found that the squared off grip of the WALTHER PP made recoil more tiring in .32ACP than shooting the SIG 232 which was lighter and used more powerful .380ACP ammo. I could feel the squared edges banging against the web of my hand when shooting.
Strangely enough, I found the recoil less fatiguing when shooting .32ACP in the smaller PPK pistol which has a shorter grip. I attributed this to the lighter slide of the PPK which is about a half inch shorter and an ounce or so lighter.
While the SIG had better sights, the WALTHERS are usable. All three pistols can shoot well and I found my qualifications scores were good with all of them. The SIG however was shooting more powerful ammo and usually scored a little higher.
The PPK had the advantage of being smaller, so I used to carry it fairly often until I bought a GLOCK 42 for my pocket gun. I was very reliable and well made ( a pre-war gun) with a usable trigger and small sights.
I would use any of them, but I kept my PPK, but in the end I sold the PP and replaced it with a second SIG 232.
All three are very good pistols, but I think the SIG 232 is just one of the best .380ACP pistols ever made. Only the BERETTA Cheetah series, the model 81, 82
84 and 85 are as good and they are bulkier.
Jim