1. Asynchronous vs Synchronous Execution: Project Reactor is known for its asynchronous, non-blocking programming model that allows for efficient handling of large volumes of data streams. On the other hand, QueryDSL primarily focuses on synchronous execution, which may not be as performant when dealing with high-concurrency scenarios.

2. Functional vs Type-Safe Querying: Project Reactor provides a functional programming paradigm for composing and manipulating data streams, making it ideal for reactive applications. In contrast, QueryDSL offers a type-safe way to construct queries in Java, ensuring compile-time safety but potentially resulting in more verbose code compared to the functional approach of Project Reactor.

3. Reactive Programming vs ORM Library: Project Reactor is a reactive programming library that excels in building event-driven, responsive applications by leveraging the concept of data streams and functional transformations. QueryDSL, on the other hand, is primarily used as an ORM (Object-Relational Mapping) library for constructing SQL queries in a type-safe manner, making it more suitable for traditional database interactions.

4. Publisher-Subscriber Model vs Criteria API: Project Reactor employs a publisher-subscriber model where data producers push events to consumers, enabling efficient handling of asynchronous operations. QueryDSL, however, provides a Criteria API that allows for creating complex database queries in a fluent and type-safe manner, providing more flexibility in constructing queries but potentially lacking the reactive nature of Project Reactor.

5. Spring Integration vs Integration with JPA/Hibernate: Project Reactor seamlessly integrates with the Spring Framework, offering reactive support for building microservices and web applications. Conversely, QueryDSL interfaces well with JPA (Java Persistence API) and Hibernate, providing an additional layer of abstraction for building and executing database queries.

6. Performance vs Type Safety: Project Reactor prioritizes performance and scalability through its reactive programming model, while QueryDSL emphasizes type safety and compile-time validation of queries. Depending on the requirements of the project, developers may choose between the performance benefits of Project Reactor or the type safety assurances of QueryDSL.

In Summary, Project Reactor and QueryDSL differ in their approach to asynchronous/synchronous execution, functional/type-safe querying, reactive programming/ORM capabilities, publisher-subscriber model/Criteria API usage, integration with Spring/JPA, and the trade-off between performance and type safety.