Although anything goes regarding engagement rings, general styles seem to change about every decade or so. Looking at the past century, the first ten years from 1900 - 1910, known as the Ewardian Era, saw ornate platinum filagree rings with Diamond accents.
The 1920's - 1930's reflect the Art Deco period which is known for geometric lines and patterns. Platinum and white gold were now the metals of choice and rings were bold with multiple Diamonds and often colored precious stones.
Because the war made platinum difficult to obtain in the 1940's, yellow gold was the new look with more of a central or solitaire Diamond.
The 1950's followed the same pattern but with slightly larger Diamonds.
The 1960's brought a cleaner and sleeker look.
The princess cut became popular in the 1970's, along with bolder more modern looking settings.
Princess Diana inspired the engagement ring of the 1980's with colored gemstones set in white gold. Yellow gold solitaires with angled shoulders were another popular choice.
Marquise cuts were first choice in the 1990's, and white gold began to make a comeback.
The ushering in of 2000 brought the cycle almost full circle with more traditional styles of white gold and platinum in vogue with cushion cut stones in halo settings on narrow bands.
Trends will continue to come and go but your ring will last a lifetime so choose your own style. Antique rings are always sought after and can make valuable heirlooms.