The Lanchester and Sten are good but held back by the magazine. The Sterling is superb and its magazine is unmatched to this day. The Thompson is also a very impressive classic SMG. When you walk into a room with a Thompson, you own it.
The Sig MPX is a modern modular design. It has a lot of nice features. I am still not 100% comfortable with it, but it makes me see how dated the MP5 has become. The bolt hold open and flared magazine housing are a big help when you’re looking through a soda straw and down to using basic motor skills. It hasn’t become famous yet and the cost is very reasonable.