The best platform to build an MVP app it is depends totally on your project requirement, cost of your project, & time-to-market goals. 

For many startups, no-code/low-code platforms like 

1. Bubble

2. Glide

3. Adalo 

And it works well for fast prototype design. For more control & scalability, React Native or Flutter are ideal for mobile applications, while Next.js or Node.js suit web apps. If AI is involved with platforms such as Streamlit / Python with FastAPI helps to build quick MVP apps. Choose a platform that balances speed, flexibility, & ease of iteration.