Round Brilliant cut diamonds are the most popular and hold their value more than any other cut diamond. Now, other diamond cuts can be more expensive, but consistent value is the Round Brilliant!
You can see no matter what size the center stone, they are all gorgeous! Remember 58-59 facets per Round Brilliant cut and if you have added stones down the shank, side stones, or a halo, that means all the more brilliance (return of white light aka small headlight) from your ring. (wink!)
Take a look at some of these examples in order of appearance .50ct center, 1ct center, and 2ct center: