Gold has been used as a measure of value throughout historical times. It is malleable, easily melted and alloyed, and in its purest form it doesn't oxidize, corrode or tarnish. Although scarce, it's not rare and can be found in many places around the globe. Gold is easily measured and divided. Gold has an internationally recognized intrinsic trading value.
Jewelry quality diamonds are valuable because of modern advertising. They are the product of modern technology and have only been around for a century or so. The value of a diamond is dependent on a technical evaluation of 4 or more factors that results in an estimated market value determined by a competent appraiser. Because diamonds are so variable in nature and their value is so arbitrary, prices are purely market driven: how much will you take for the diamond you are trying to sell?
Of course, its hard to find one and only diamond necklace all of them are so different and marvelous! So, the first thing to pay attention to is your feelings while wearing them https://www.itshot.com/jewelry/womens-necklaces/diamond . Only your intuition can tell you which one is for you: a classic necklace with diamonds or an experimental piece of jewelry with different gemstones.