What's also nice is that you can create color themes in their Color/Kuler web app and then have those themes available to pick from within XD, or that you can open and work on images and scenes in Photoshop or Dimension (their V-Ray based 3D app which is cool for Hero scenes).
Best use both, Figma is better for web apps (XD doesn't even have inset shadows for forms), and XD is a bit better for landing and marketing pages, especially if you use their other tools.