Mederma made my scars red, puffy and itchy.
I went to the doctor for a very large scar and got a cream that reduces the size of the scar tissue by thinning the skin. It sounds weird but it was painless and actually worked a bit. I'm going to see a dermatologist about it now which IMO is the best thing to do.
All the over the counter products I've used that promised to reduce my scars in someway have irritated them more than anything. I now only use a soothing cream that is actually advertised for stretch marks. it works really good.