I think the cushion may have a little more fire and sparkle than the radiant of the same quality. Round brilliants supposedly have the most sparkle because of the faceting, and the cushion is going to give you a similar sparkle in a more "squared" shape. It also has a nice vintage feel which is very popular right now, but will also look great for many years. You might also look at the Tiffany Lucida cut. Something else to consider is the size of the stone. If you are looking in a 2 carat range, that won't be an issue. But on smaller stones the cushion may lose some "presence" compared to the radiant. I would look at both in person. You will find that one stone speaks to you over all the others!