I tried the mederma stretch mark stuff for some light marks on my thighs and boobs and I'm really not sure it works because I couldn't manage to use it for very long because I thought it smelled HORRIBLE. It smells nothing like normal mederma, which I think is fine. It's a crazy strong powdery floral scent plus, idk, chemically. I'll put some on occasionally when I spend nights alone (so no one but me has to smell it), but I've mostly resolved to dealing with what's there and using lots of cocoa butter products. No idea how well normal mederma works on stretch marks as opposed to other kinds of scars.
The palmer's Tummy butter smells FABULOUS. The stuff in the tub, not the bottle. It's harder to use though, and I'm not really sure how well it works. It doesn't do much for the appearance of my marks, but that might be because mine are pretty faint anyway.
That said, I was watching an episode of the British version of How to Look Good Naked and they do product testing and they did one for stretch mark removal products and said the new Nivea product got the highest ratings from their testers.