Newtonsoft.Json and System.Text.Json are the primary JSON libraries in the .NET ecosystem.
System.Text.Json outperforms Newtonsoft.Json in terms of speed and memory usage when handling large datasets.
Newtonsoft.Json has a more extensive feature set and is suitable for complex JSON processing, while System.Text.Json focuses on performance and security.
Choosing between the two libraries depends on project requirements, performance needs, and ease of use.