The feng shui criteria of good or bad jewelry are based on the energy created by diamonds and other crystals and gemstones in their specific setting. If you look at the history of engagement diamond rings, you will see many different stones, as well as designs; most with deep meaning and their own complex language. For example, sapphires have been used because of their association with loyalty and devotion, rubies because of their passionate energy and emeralds for vitality and good luck.
The diamond is the "king of stones" because it is one of the strongest and most light-filled gemstones in nature; it has strong protective and healing properties, so it is a perfect symbol to express love for a lifetime. The energy of the diamond is considered to instill the aspect of trust and fidelity in one's relationship.
Feng shui-wise, a traditional engagement ring with one diamond is the best, as it speaks of "the one and only." Also, the feng shui energy of a bigger stone—in this case, a diamond—is stronger than the energy of a group of smaller ones.
One big diamond with several little diamonds on the side is also good feng shui, much better than a ring with three diamonds. Three is not the best number for stones in the engagement diamond ring design, just like a prominent number three is to be avoided in a couple's bedroom decor.
A Feng Shui Disclaimer
Know that it is always best to trust your own feelings when you choose good jewelry. There are so many beautiful jewelry designs on the market, some of them with better feng shui than others, so the specific design will be your main criteria to assess. These are general feng shui guidelines; you are the one who knows how to make the best choice with the designs you have in front of you. Trust your heart to choose the best design.