For solo users or teams looking for quick ideation and sketching, Excalidraw is your best bet. Its charming hand-drawn aesthetic makes it perfect for brainstorming sessions and initial architecture sketches, allowing for an intuitive flow of ideas. However, if you seek polished visuals or a comprehensive design tool, you should avoid it, as its low-fidelity nature and limited features won't meet those needs.
On the other hand, if you're part of a privacy-conscious team that values open-source solutions, Penpot is a strong choice. It offers a more structured design and prototyping environment with real-time collaboration features. While it lacks the extensive plugin ecosystem of more mainstream tools, it's ideal for those who prioritize open standards and self-hosting capabilities. Opt for Penpot if your focus is on design and prototyping while being mindful of privacy, but steer clear if you require the highest polish or advanced integrations like those found in Figma.