I don't think that there is one specific type of OTC scar treatment that's good. I think that any scar product with healing ingredients and moisturizers will work well.
The issue is that most people assume that when they use a scar treatment, the scar will go away overnight. That's never the case though. It takes time for scars to go away and the type of scar treatment used might not make much of a difference in this regard. It's important to use a scar treatment regularly as directed. Quitting too early or not applying the product frequently enough will prevent it from working.
I'm partial to scar treatment sheets, but the type of product is really a personal preference.