There are a few options when it comes to the best software for UI/UX design (the creation of mockups and prototypes in particular). The most popular are:
The goal of any designer is to develop the best UI and develop the best user experience possible, and you want the best tool to help achieve this. Figma is the ideal design tool - highly collaborative, accessible cross-platform, and cloud-based. In addition to these features it comes with a huge suite of unique design tools. The auto-layout feature, for example, helps designers craft highly responsive products in a way that reflects actual CSS properties like grids and flexbox which serves to ease the transition between design and development.
Note: One tool doesn't always replace the others! Figma does not include the print design and photo editing features of Adobe Photoshop and other software also used by designers. Photoshop is the industry standard in raster (pixel-based) graphics editing, photography and digital art. Adobe Illustrator, on the other hand, is the standard vector-based design tool used for print design, logos, icons and more. All of these tools have a place on a designer's belt!