What is better to use for adult acne that is beginning to scar, the salicylic acid peels or the glycolic acid?

Either: Either peopling agent depending on which is better tolerated accomplish the same peeling effect . Both vary in strength and the higher the strength the greater the peeling effect. This needs to be combined with dietary changes, oral zinc supplements, and topical antibiotic creams.

Depends on skin type: Both are good options depending on your skin type. I prefer salicylic acid in most acne patients as it is drawn more towards oily areas and helps a bit more with discolored spots left after acne resolves. There are also combination peels with various concentrations of both ingredients. You will want to find an experienced provider who can properly evaluate you and make the best recommendations.