So I was playing Pokemon Legends Arceus like a competitive player ,that's when I thought of adding Hisuian typhlosion or infernape .So which one is better?
Infernape is definitely better than Hisuian Typhlosion. Infernape has a better movepool and stats. All of Typhlosion's coverage moves are physical, which is bad for a special attacker. In a game like Legends: Arceus, you want all the power you can get along with the speed. Here's a moveset you can use for Infernape.
Infernape Nature: Jolly / Adamant - Flare Blitz - Close Combat - Mach Punch - Rock Slide / Thunder Punch