The DP27 is a guilty pleasure of mine too and not having to belt-feed is a cool change of pace for the class; handles like a dream albeit looks the part of a crossbow with the pan magazine, IMO.
The MP 40 is unquestionably the working man's SMG, getting results no matter the plan or problem and much like its RL counterpart – the bread and butter of Nazi infantry, I've read. I can't use it because I like to shake up meta so my affaire has been rather with the PPSh-41. I have a CQC build around the PPSh with decoy frags that has me clearing rooms like a professional mover, especially on map Eagle's Nest. Woo! If I see Guard Dogs deployed though, I run – I know you'll feel me on that. The M1928 was my favourite in-class before that.
I tried to max the Automaton during the last XP event but I don't walk away from firefights I should with it, IMO, so I always shy away from committing. For mid, I went back to my AS44 (or DP27), but I'm still learning some of the ARs in this and what their personalities are, for example, the Volk has been really, really fun but doesn't trade well (for me) and right now I'm applying everything I know from MW's FR 5.56 to Vanguard's Itra AR without having explicitly danced with it yet. I primarily play MMRs and snipers so it'll take me a while to work through all the assault options in this. I'm excited for the Vanguard store to launch so I can see what vanities await my loadouts.