The best gun in Call of Duty WW2 has to be good at everything and be easy to use at the same time. It must be able to hold down objectives, clear out close quarters and provide support from medium range. The MP-40 submachine gun is good at close range, where it easily beats most assault rifles, and is very competitive with assault rifles at medium range. It is easy to use and a good all around weapon.
However, there is an assault rifle that is just as good as the MP-40 at close range and even better at medium range. The STG44 is very strong at close and medium range due to the high fire rate and low recoil of the STG44. It can be used in any situation and is pretty good even in the hands of a novice. Therefore, the STG44 is the best gun in Call of Duty: WW2.