Hi kennyames,
It would depend on the specifics of the materials inside each mattress you are comparing but if you are making an apples to apples comparison between two mattresses that both use the same type and quality of materials inside them then the two sided version would be significantly more durable than the one sided version of the same mattress (provided that it is flipped and rotated on a regular basis).
There is more about the pros and cons of one and two sided mattresses in post #3 here and the posts it links to.
Phoenix