Actually, Retin-A works to make your scars look better. It takes a while, but it is like a gradual skin peel.
Your skin will be dry and peel, but it will make the tone and scars look better in the end.
Personally, I don't have any experience with Mederma, but other people on here have used it, and said it doesn't work.
Do a search for mederma/ acne scars on this site.
GL