IMO they're both severely overweight for a pistol caliber carbine, by at least 2 or 3 pounds. The ergonomics on both are not good, and I think both designs are not as durable or reliable as the weapons they were modeled on due to adapting them to work semi-auto. IMO the PPSh-41 is plenty simple, and low-maintenance but if you were gonna go for a pistol-caliber carbine styled after a WWII SMG, I'd see if you can find one of those PPS-43 carbines, they were available in both 9mm and 7.62 Tokarev, but lighter and handier than either the Suomi or the Shpagin. Although honestly I cannot say for sure if they are still being made.
"My momma, she done told me, there's heart and then there's hate
If one of 'em's inside of you, the other one, it aint."