in my experience with both guns the MP40 seemed like the more versatile weapon, its lower fire rate helps aim it better well causing it suffer in more panic stricken situations, it also feels like it packs a punch at greater range, this means that even on larger maps you can actually use it to suppress or even kill the enemy effectively. the PPSH-41 is better suited for CQC and cause of its insane fire rate which makes it the perfect "oh s**t" weapon, its basically shreddy confetti on any kraut at up to 30m (ish). so basically think the MP40 as the utility weapon that's good in most situations, well the PPSH-41 is basically the shock troopers delight since it murders all other weapons in close quarters (not including a panicked out of position machine gunner)