I agree that Leao might be a better option for Manchester United than Lookman. The two are good players but Leao proved himself in AC Milan many times and could adapt perfectly. I have some worries that Lookman will be the new Victor Osimhen, he needs to learn from his Nigerian teammate who was once, one of the best players in a season then he faded.
It depends on the position you want to fill because both Lookman and Leao are good on the wings but Leao leans more on the right and Lookman on the left.
When Manchester United try to sell Rashford maybe Leao could be an option but when the option is Rashford will be replaced by Garnacho maybe the position for Lookman is more worth it because Antony can't play well on the left wing but in the end the characteristics of these two players are quite good indeed because they can play in several positions tactically it makes it easy for them to be placed anywhere to be in the striker or in the winger especially the goal scoring instinct is also quite good.
I think both of them can be better options but when the element of closeness maybe Lookman is still very approachable especially there is Hojlund who has played together at Atalanta even though only briefly so this can be a good approach option especially Leao is very difficult to approach because Milan protects this player more.