I'd like to see the formation which plays on our strengths, not weaknesses.
We need to maximise Bruno, Pogba (yes, he still is our top tier player and if we don't cash him this summer, then we need to squeeze him as much as we can), Sancho (if he arrives) and Rashford. Other players have roles which are obvious (Shaw is LB, Maguire is CB and not a DM etc), but these attacking players are more dynamic and needed to be found the right role and position on the pitch.
If Rashford is his best (at first, he needs to become injury-free and take a long rest or reduce the workload), he is on the left side, combining with Shaw. Bruno is better as a 10 and not an 8, Pogba is better as an 8 not a 10.
According to this logic, a 4-2-3-1 is reasonable, right? A 4-3-3 might damage Bruno, as he plays lower, but that makes Pogba better (supposedly). Sancho, I don't understand whether he'd be better or worse in these formations - a pure winger or a wide forward.