1. Syntax: Nim uses a Python-like syntax with significant whitespace, making it more readable and concise. In contrast, Vala uses a syntax that closely resembles C# and C, which might be more familiar to developers coming from those backgrounds.

2. Performance: Nim is known for its excellent performance, often matching or outperforming C and C++. On the other hand, Vala, being a high-level language, might not be as performant as Nim in some cases due to additional abstractions.

3. Metaprogramming: Nim has powerful metaprogramming capabilities, allowing for advanced code generation and manipulation at compile time. Vala, while supporting some metaprogramming features, may not be as flexible or extensive as Nim in this aspect.

4. Memory Management: Nim provides more control over memory management through manual memory allocation and deallocation if needed. Vala, on the other hand, relies on GObject reference counting for memory management, which can be less flexible in certain scenarios.

5. Library Ecosystem: Nim has a smaller but growing library ecosystem compared to Vala, which benefits from its close integration with the GNOME project and its extensive libraries. Developers looking to leverage existing libraries might find Vala more suitable in this regard.

6. Target Platforms: Nim can compile code to various platforms, including JavaScript, while Vala typically targets the GNOME platform and Linux systems. This difference in target platforms can influence the choice of language based on the intended deployment environment.

In Summary, Nim and Vala differ in syntax, performance, metaprogramming capabilities, memory management, library ecosystems, and target platforms.