Foden and Rashford are better in front of goal, even though Rashford has his periods where he cant hit a barn door.
Foden is better supporting the attack. Saka has good assists this season as Arsenal have been very good, but in any other year Foden beats him despite rarely playing in his best position. He is also better at the interlinking play City's forwards specialise in.
Rashford is more direct and better at getting in behind defenders.
For me, Saka is a good player who will be hyped to the hills for a couple of years before coming back down to earth. A bit like Raheem Sterling was.