Is it better to combine vit C or retinol with 25% Glycolic Acid? Which percentage? I've got adult acne and combination skin

Retinol. Retinol is a vitamin A derivative, as is Retin A (tretinoin) which is helpful for many types of acne. I would also see a dermatologist, as there are many prescription products which may be more helpful. Hormonal imbalances are fairly common in adult acne and this should also be addressed.
Retinol. Is proven to mature skin and cure acne. Vitamin C is an organic acid in this context without more effect than domboro soak. I actually did both at your age--before there were better prescription ones like TAXORAC (sp). Vitamin A worked; soaks/antibiotics etc did not.