The two players are the two most expensive footballers in history, with the former switching from Barcelona and the latter arriving from Monaco.
Neymar has scored 32 times in his 35 appearances for PSG, while Mbappe has managed 25 goals in 47 appearances for the French giants in all competitions.
Despite Mbappe being seven years younger than Neymar, Simeone has revealed that he would choose Brazil's captain due to his greater tactical understanding of the game.
"Neymar. In the Barcelona team of Luis Enrique, when he needed to work, he worked. Mbappe is more individualistic and doesn't have a definitive role. Neymar has a fixed position," Simeone told Cadena COPE.
Mbappe helped France win the 2018 World Cup, while Neymar's Brazil side crashed out to Belgium in the quarter-finals.