Selecting a UI component library is crucial for long-term app development. Factors to consider include customization capabilities, open source or closed source options, modularity, longevity, maintainers' dedication, compatibility with tools like React Testing Library and Jest, accessibility support, popularity, and performance. Libraries such as Radix UI, Chakra UI, MUI, Shadcn UI, and BluePrint UI offer varying features and benefits. It is essential to choose a library that aligns with the specific needs of your project and organization while keeping future scalability in mind.