If you're an open-source advocate or part of a privacy-conscious team, choose Penpot. It offers a genuinely open-source experience that allows for self-hosting and is built on open standards, making it designer-developer friendly. However, be prepared for a smaller ecosystem and slightly less polished performance compared to more established tools like Figma.
On the other hand, if you’re a frontend developer or an indie hacker looking to quickly generate working UI from prompts, v0 is the better option. It produces actual React/Tailwind code, allowing for fast iterations that pair well with modern web stacks like Vercel and Next.js. Just be cautious of its credit-based pricing if you plan to use it heavily, and remember that it's not suitable if you don’t utilize the React or Tailwind frameworks.