I used both and am covered in stretch marks. I asked my doctor about it once and she said it might do you good to keep moisturized but anything else is a waste of money and you're more likely to know if you're going to get stretch marks by looking at the ladies in your family.
I bought compressed vitamin E oil off Amazon.. it was so compressed that I had to mix it with some lotion to get it on. Ended up buying Palmers tummy butter to mix them both. Currently 40 weeks pregnant today and thankfully no stretch marks at the moment. I definitely recommend that oil.. some people use it for after and they are great reviews on removal. Super cheap too!!
I bought "bio oil" I haven't got to use it yet but I heard it works great!
I used cocoa butter my entire pregnancy and managed to get stretch marks at 38 weeks:( I'm 3 months pp and I now use Palmers tummy butter for stretch marks every time after I shower. I massage it into my skin for a few minutes. They are now smooth and they are starting to lighten up.