1. Programming Languages and Platforms: Entity Framework Core is primarily focused on the .NET platform and supports programming languages such as C# and VB.NET. On the other hand, SQLAlchemy is mainly used with Python and supports multiple databases, including popular ones like PostgreSQL, MySQL, and SQLite.

2. Fluent API vs. Declarative Approach: EF Core uses a fluent API approach, where developers define the database schema and relationships using method calls in code. On the contrary, SQLAlchemy follows a declarative approach, where developers define the database schema using class definitions. This allows for more concise code in SQLAlchemy.

3. Database Support: While EF Core supports various databases, including SQL Server, PostgreSQL, and MySQL, it has limited support for NoSQL databases. SQLAlchemy, on the other hand, provides explicit support for both SQL and NoSQL databases, making it a more versatile choice for handling different types of databases.

4. Query Generation: EF Core provides a LINQ (Language Integrated Query) querying mechanism that allows developers to write queries in a strongly-typed manner, using language constructs like lambdas. SQLAlchemy, on the other hand, supports its own querying language called "SQLAlchemy SQL Expression Language", which empowers developers to write complex queries in a more flexible and powerful way.

5. Maturity and Community Support: Entity Framework Core is a part of the Microsoft ecosystem and has strong support from Microsoft and the .NET community. It benefits from continuous development and improvements. SQLAlchemy, being a widely-used ORM in Python, also has a vibrant community and extensive documentation, but it may not have the same level of integration and support as EF Core within the Microsoft ecosystem.

6. Performance Considerations: EF Core has made significant advancements in terms of performance and optimization over its predecessor, Entity Framework (EF). However, SQLAlchemy is known for its performance and scalability, especially when it comes to handling large datasets. SQLAlchemy allows developers to fine-tune and optimize queries for better performance in a more granular way compared to EF Core.

In Summary, Entity Framework Core (EF Core) is primarily focused on the .NET platform and uses a fluent API approach, while SQLAlchemy is mainly used with Python, supports multiple databases, and follows a declarative approach. EF Core has better integration within the Microsoft ecosystem, while SQLAlchemy offers more versatility in terms of database support and query writing capability. SQLAlchemy is known for its performance and scalability, especially when handling large datasets.