The main difference between these two types of cuts comes down to the amount of sparkle the diamond displays.
Step cuts emphasise the diamond’s clarity with a clear, open look deep into the stone. They are more passive in their beauty and have a minimalist aesthetic. While they still have very good sparkle, this is a bit more subdued.
Brilliant cuts, d'autre part, are mathematically designed to enhance the sparkle. They have more facets than step cuts, and their facets are shaped differently – typically triangular and kite shaped.