I think Lingard is fantastic - however I see Lingard getting the ball in positions where Martial has better capacity to take on the players in front of him.
These positions that Lingard get in to his due to his fantastic positionining - but saying that Martial would only need to to position himself few times a game to be absolutely clinical with his chances.
Lingard is better for a defensive alternative to our attack - possibly even being the highest forward player that puts pressure. Lingard as an attacker is a player that I call a 'pivot' player; he either makes short passes to interchange & pass the ball to attackers around him or he tends to position himself to the point where the attackers around him have less defenders to deal with. Lingard is a pivot that helps the players around him even if he doesn't particularly rack up numbers.
However when we don't need it it's better to have a player like martial drop deep centrally to receive the ball and start our attacks. He can get the numbers, he can come deep, can make short passes & can take the Central defenders on with ease.
The Firminh0' goal where he takes 2 defenders on in to open territory is p*ss easy for a player like martial more so than any other player. In my eyes players who have to defend against martial are always in a 50/50 position of either taking him on or leaving him be. On the wings martial can be allowed to go past the fullback but still is in a position where he can't properly attack - ie being out too wide; but centrally & deep - martial has the ability to come at the CB's with pace and the ball at his feet; having the ability to beat them with a single piece of skill before being one on one with the GK.