If you're part of a product team focused on building custom canvas applications, tldraw is your best option. Its polished infinite canvas allows for real-time collaboration, making it ideal for developers who want to create intricate designs and UI components. However, keep in mind that it isn't entirely open-source, and any commercial use will require a paid license to remove watermarks.
On the other hand, if you need a robust tool for collaborative interface design among product designers or design teams, Figma is the clear choice. Its strengths lie in real-time multiplayer design capabilities and a rich ecosystem of plugins and templates. While it can get pricey for larger teams and may struggle on lower-end machines with heavy files, the benefits far outweigh these limitations for serious design projects. Avoid Figma if you need an open-source tool or require full offline functionality.