If you're looking for a tool that allows quick brainstorming and lightweight sketching, Excalidraw is the best choice. Its hand-drawn aesthetic makes it perfect for developers sketching architecture or jotting down ideas rapidly. Being free and open-source, it’s also great if you prefer data to stay local. However, if you need polished designs or more advanced features, Excalidraw isn't suitable, as it’s intentionally low-fidelity.
On the other hand, if you're part of a design team or working on intricate product design, Figma is the way to go. Its real-time collaboration and extensive plugin ecosystem make it ideal for tackling complex projects with multiple stakeholders. Just be aware that Figma can become pricey for larger teams and may strain lower-end machines, and it doesn't offer offline functionality like Excalidraw. Choose based on whether your priority is simplicity and local work or robust collaborative design capabilities.