I guess it is a reasonable question. Despite Rashfords slightly better season I would still say Salah based on the fact that between Nunez and Gakpo we have those type of qualities that Rashford has. Salah gives you something unique, those Messi esque tendancies that Rashford could only dream of.
That's my stance. There will be a time, as Mo declines and if Rashford can maintain his form from last season, when the answer will inevitably shift. But not now and not when Rashford still has a lot to prove.