A slender band with a single diamond, the solitaire -- especially a round stone -- is the ultimate in classic engagement ring styles. Both graceful and elegant, this ring complements any woman's hand and will never go out of fashion. As with any engagement ring, the composition of the band can affect the overall price and quality. Platinum is the most durable metal available, although it has a steep price tag. Yellow or white gold are beautiful as well and significantly less expensive, although gold does wear away over time and is more likely to sustain damage than platinum.