Diamond or cubic zircona OR 1 diamond or 100 cubic zirconas? In my opinion i would always go for the real thing but then again i have had the 100 cubic zirconas and although they were lovely they are, ultimately disposable and not worth much unless they have sentimental value.
With real diamonds, pearls or precious stones you treasure them as an investment piece or as a family heirloom. They can be passed from generation to generation or sold at a later date as genuine jewellery can often go up in value.