Xamarin is highlighted as a leading framework for multiplatform app development due to its ease of use, speed, cost-effectiveness, and support for the DRY (Don't Repeat Yourself) principle. It allows developers to share up to 90% of their code across different platforms, ensuring faster development and simpler maintenance. As an open-source solution backed by Microsoft, Xamarin offers robust support and access to native APIs, making it a compelling choice for building high-quality applications.