Of all the guns that would seem to fit into the SMG category I like the Suomi m31 best of all. It's almost a gun that I can not really make up my mind what it is exactly due to the long ( for an SMG ) barrel. I like it because it is made from a solid lump of high quality steel, and has been made with great precision by skilled craftsmen. It is the only gun I know of that has a vacuum valve in the receiver cap, this reduced the rate of fire to a mere 980 ish rounds per minute

as the valve closes on the forward stroke of the bolt. It could only work because of the tight tolerances. I think they were made into the mid 50's, but they were very expensive to build, probably the most expensive of all the SMG's used in ww2,and that put an end to their production. The Russians found out all about them the hard way and developed their own cheapo alternative, the PPSH 41, which really is a piece of junk compared to the Suomi ( Finland ) SMG.
I had one deactivated Suomi until today, now I have three LOL. I don't know what I'm going to do with them all, but I just could not resist. They are selling here for just 279 in UK pounds.