My pick would be the M2 carbine, followed by the M1, followed by the Ppsh-43. It all comes down to the ballistics of the .30 carbine for me. When compared to the '06 rifle cartridge the .30 carbine is a massive compromise, but compared to a 9mm or .45 you gain far more range.
Of the WW2 and early cold war subguns, I own the M2, M1A1 Thompson, Swedish K, and Sterling. The Swedish K and Sterling are amazing guns but didn't serve in the war. The M2 is a great little blaster for approx. 80-100 rounds of full auto burst fire. After that it overheats and becomes unusable. I'm convinced that the full auto feature on these was for emergency purposes, sort of like on the Reising. It's an excellent PDW that can be forced to play the role of SMG for a few mags if necessary.