Retin-a was the only thing that seemed to make a marked difference on fresh stretch marks. It will do nothing on older stretch marks. It took me 2-3 weeks to see some fading.
I've used vitamin-e before, but I can't really say if that helped, or if they were fading on their own. It was a pretty slow process with that.
The stretch marks which I used retin-a on are much less noticeable than those I didn't use it on. I used the 0.1% concentration, and it even helped on some of the deep fucking tears I had. The advantage of the retin-a definitely diminishes with the age of the stretch marks. Try to catch them when you first see them forming.