This is a comparison of 1.5 ct ideal cut, E color, VS2 clarity, round diamonds (click the dollar amount to be taken directly to the diamond):

James Allen: $16,730

Blue Nile: $18,082

Brilliant Earth: $18,120

Abazias: $20,424

These diamonds are independently inspected and graded by GIA/AGS, which means you can trust their quality. The quality of these diamonds is identical--the only thing that is different is the price.