Choose NestJS if:

• You're building a large-scale, enterprise, or microservices-based application.
• You prefer TypeScript and want built-in features like DI, validation, and modularity.
• You need native support for GraphQL, WebSockets or event-driven architecture.

Choose Express if:

• You're building a simple app, prototype or MVP.
• You need complete flexibility and prefer minimal abstractions.
• Your team is already experienced with Express or you're integrating with an existing app.

NestJS is ideal for complex, scalable and enterprise-grade apps, 
While Express is better suited for lightweight, quick and simple projects.