I am always leery of these best/worst equipment lists. Every weapon design--tank, firearm, aircraft, warship--is a balance of different characteristics. No weapon can do everything equally well, and you can't have everything in the same design. When evaluating a weapon you always have to bear in mind the tactical function it was designed to fulfill, as well as the military situation at the time and the needs of the given nation's armed forces. SMGs are a good example of this. First generation guns like the Thompson and Lanchester were well-built, pretty reliable, and had a lot of inessential but nonetheless useful features: selective fire, compensator, bayonet lug, etc. This was all right in the conditions of the 1930s, but by 1941-42 the British and US armies needed masses of inexpensive guns which could be produced cheaply and quickly and mastered easily by conscripted civilians. The resulting weapons (Sten, M3) were frailer than first generation guns and perhaps less accurate because of the lower weight, but they were simple, compact, light, fast-firing, inexpensive, and so available in large numbers when they were most needed. Within the different generations of SMGs some were of course more effective than others; I'd take an M3 over a Sten any day.