IMPORTANT: what is better to use to cover up scars? Liquid, powder or solid foundation? ?

Basically it's my prom on Saturday and I really want to look pretty because the guy I love is gonna be there and yeah...but I have a bunch of scars on my arm :/ and should I use liquid, or powder or like foundation that you apply with a sponge (kinda solid foundation) ?? Also lighter or darker than my skin tone?? Thanks :)