In contemporary software engineering, APIs (Application Programming Interfaces) play a pivotal role in facilitating seamless communication between diverse systems, enabling modular development, and supporting rapid scalability in enterprise applications. Enterprises today are increasingly adopting complex, large-scale systems comprising multiple microservices, distributed databases, and cloud-native architectures, necessitating robust, efficient, and flexible API solutions. REST (Representational State Transfer) and GraphQL represent two prominent paradigms for API design, each with distinct architectural principles, operational models, and developer ecosystems. REST APIs, rooted in the principles of statelessness and resource-oriented architecture, have long dominated enterprise software development due to their simplicity, standardization, and compatibility with HTTP protocols. They facilitate clear endpoint structuring, caching mechanisms, and straightforward versioning strategies, making them suitable for traditional enterprise applications with well-defined data requirements. However, REST faces challenges in modern dynamic enterprise environments, particularly concerning over-fetching or under-fetching of data, the proliferation of multiple endpoints, and rigid versioning structures that may hinder agile development. GraphQL, introduced by Facebook in 2015, offers a compelling alternative by enabling clients to request exactly the data they need through a single endpoint, improving efficiency and reducing network overhead. Its query language, type system, and schema-driven design allow enterprises to create highly flexible and adaptable APIs, particularly suitable for complex systems where data structures evolve rapidly, and multiple clients consume diverse datasets. Despite these advantages, GraphQL introduces complexities in caching, query validation, and backend orchestration that enterprises must carefully manage, especially under high-volume transactional workloads. This paper presents a comparative analysis of REST and GraphQL APIs in the context of large-scale enterprise applications. By examining criteria such as performance, scalability, flexibility, security, developer experience, and cost implications, the study provides a nuanced understanding of the relative strengths and weaknesses of each approach. Additionally, it draws insights from empirical studies, industry benchmarks, and case studies from real-world enterprise implementations to provide practical guidance for decision-makers. The findings reveal that while REST continues to be ideal for systems prioritizing simplicity, standardization, and mature tooling, GraphQL excels in environments demanding dynamic queries, fine-grained data retrieval, and enhanced client-side flexibility. Enterprises must therefore align their API strategy with organizational goals, application complexity, and developer capabilities. Ultimately, this research underscores the necessity of a strategic, context-aware approach to API selection, ensuring that performance, scalability, and maintainability objectives are met in large-scale enterprise deployments.