There is no objectively "best" diamond shape — it's a matter of personal preference. Round brilliant diamonds offer the most sparkle and are the most popular, but each shape has its own unique appeal. The best shape is the one that speaks to your personal style.

Round shape diamonds are typically the most expensive shape due to their high demand. The precision required to cut a round diamond to achieve optimal brilliance also contributes to its higher price.

Diamond shapes that maximize surface area, such as marquise, oval, and pear, tend to look larger than other shapes of the same carat weight. These shapes elongate the diamond, creating the illusion of a bigger size. Choosing a shape with a larger table facet can also enhance the diamond's apparent size.

Fancy cut diamonds include any shape other than the standard round brilliant. The term encompasses princess, cushion, emerald, asscher, oval, marquise, pear, radiant, and heart shapes.

Elongated diamond shapes have a rectangular or oblong appearance rather than square or round. These include oval, pear, marquise, elongated cushion, elongated radiant, and emerald cuts. These shapes create a slimming effect on the finger and often appear larger than other shapes of the same carat weight due to their larger surface area. Popular length-to-width ratios for these shapes range from 1.2:1 to 2.0:1, depending on the specific cut.

The round brilliant diamond is the most popular shape, chosen for its timeless appeal and unmatched brilliance. Its versatility and classic design make it a favorite for engagement rings and other fine jewelry. Other popular shapes include princess, oval, and cushion, each offering unique aesthetic qualities.

Round brilliant diamonds are renowned for their exceptional sparkle due to their ideal facet arrangement and symmetrical shape. The round shape maximizes light performance, producing the highest level of brilliance, fire, and scintillation.

Diamonds get their shape through a precise cutting process performed by skilled diamond cutters who transform rough diamond crystals into polished gems. This process involves several steps:

1. Planning: Cutters analyze the rough diamond using advanced technology to determine how to maximize its value. 
2. Cleaving or sawing: The rough is separated into workable pieces. 
3. Bruting: The diamond is given its basic shape by grinding against another diamond. 
4. Faceting: Precise facets are cut and polished onto the stone. 
5. Final inspection: The diamond is evaluated for cut quality and symmetry. 

The cutter must balance maximizing the diamond's carat weight with achieving optimal proportions and minimizing flaws.

Changing the shape of a diamond is possible but involves re-cutting the stone, which can result in a loss of carat weight and potential value. This process requires skilled craftsmanship to ensure the new shape maximizes the diamond's brilliance and maintains its structural integrity. It is typically done to enhance the diamond's appearance or to repair damage.

The most widely used diamond shapes are round brilliant, princess, cushion, emerald, oval, pear, marquise, asscher, radiant, and heart. Beyond these standard shapes, several specialized or less common shapes exist: trillion, baguette, European, mine, rose, briolette, kite, tapered baguette, calf, and shield.

Elongated diamond shapes create the illusion of longer, slimmer fingers. The most effective shapes for elongating fingers include:

1. Marquise: The pointed ends extend along the finger axis, creating maximum length 
2. Oval: The elongated shape draws the eye up and down the finger 
3. Pear: Combines the elongating effect with a unique asymmetry 
4. Emerald: The rectangular shape with its clean lines extends finger appearance 
5. Elongated Cushion: Provides both elongation and soft edges 

For maximum elongating effect, these shapes should be set with the length running along the finger rather than across it. North-south settings (along the finger) visually extend finger length, while east-west settings (across the finger) can make fingers appear wider.

Certain diamond shapes can create the optical illusion of slimmer fingers. The most effective shapes for this purpose include:

1. Marquise: The elongated shape with pointed ends draws the eye vertically 
2. Oval: Creates a lengthening effect without pointed edges 
3. Pear: The asymmetrical design elongates while adding unique character 
4. Emerald: The rectangular proportions extend the finger's appearance 

To maximize the slimming effect: 

• Choose settings that position the longest dimension of the diamond along the finger 
• Opt for narrower band widths that won't visually widen the finger 
• Consider a halo setting that emphasizes the diamond's elongated shape 
• Avoid wide, chunky settings that can make fingers appear shorter or wider

In its natural, uncut state, a diamond typically forms as an octahedral crystal — essentially two pyramids joined at their bases, creating an eight-sided shape. This octahedral structure reflects diamond's crystal system and the way carbon atoms bond under extreme pressure deep within the Earth.

The majority of gem-quality diamonds found in nature have an octahedral structure, which diamond cutters must transform into the familiar polished shapes we recognize in jewelry. The octahedral shape explains why the round brilliant cut was developed — it works efficiently with the natural crystal structure while maximizing brilliance.

The round brilliant cut is widely considered the most timeless diamond shape. Its classic appeal has endured for over a century, making it a truly evergreen choice. Round diamonds have dominated the engagement ring market for generations and show no signs of losing their popularity. 

Other shapes with timeless appeal include: 

• Cushion cuts: These have been popular since the early 1900s 
• Emerald cuts: Their clean, architectural lines have remained fashionable for decades 
• Oval cuts: Their balanced design combines classic and contemporary elements 

These classic shapes have demonstrated enduring appeal across generations, making them great choices for those concerned about long-term style relevance.

Asscher and emerald cuts are typically the least expensive diamond shapes per carat. This price advantage stems from lower manufacturing costs, lower demand, and different cutting priorities (clarity over brilliance). However, it's important to note that these shapes emphasize a diamond's clarity, so you may need to select a higher clarity grade, which can offset some of the cost savings if you want a truly eye-clean stone.

There are 10 commonly recognized diamond shapes available in the jewelry market: round, princess, cushion, oval, emerald, asscher, radiant, marquise, pear, heart. Beyond these standard shapes, several specialized or less common shapes exist: trillion, baguette, European, mine, rose, briolette, kite, tapered baguette, calf, and shield. Many of these less common shapes are used as accent stones in multi-stone settings rather than as center stones.

The right diamond shape for your ring largely depends on your finger's characteristics and personal style preferences. Beyond physical considerations, your lifestyle and fashion sensibilities matter too—active individuals might prefer secure settings with rounded edges, while those drawn to vintage aesthetics might gravitate toward cushion or asscher cuts. Ultimately, while these guidelines can help narrow your options, the perfect ring shape should resonate with your personal style and feel comfortable on your finger.