Most recently, Man United beat Tottenham 1-0 at home. In this match, Rashford played for 70 minutes and was substituted to Marital. After that, it was the French player who scored for the home team.
In this 2017-20 season, coach Mourinho is somewhat prioritizing using Rashford. He has played a total of 16 matches in all competitions while Martial has 14. Rashford started 10 and Martial 7.
As for Rashford, he has scored 7 goals in all competitions, 1 more than his teammates. Every time Rashford starts, Man United's winning rate is also higher ( 90% compared to 71%.
However, in terms of scoring efficiency, Martial played somewhat more effectively. It took him about 100 minutes to score 1 goal. Martial took up to 128 minutes to make the Man United fans celebrate.
Since the beginning of the season, these two players have both had 5 assists. However, Martial was better at creating opportunities for his teammates. He has helped Man United players score 19 times, an average of 1.36 times/match. Meanwhile, Rashford's figures are 15 and 0.94 per game, respectively.
On paper, Rashford can play alongside Martial but coach Jose Mourinho rarely does this. When Man United controlled the game, he prioritized using Juan Mata or Mkhitaryan, who could launch sharp passes to disrupt the opponent's defense.
When playing counter-attacking, Man United often rely on quick attacks like they did against Tottenham recently. At that time, a speed man like Lukaku would play the highest up the attack and only Rashford or Martial would be enough to make Man United's attacks faster.
It was not until the second half of this season, when coach Mourinho gave Lukaku a break to make way for Ibrahimovic, that he could make up for Ibrahimovic's slowness due to his age by allowing Martial and Rashford to play together.