1. Architecture: Prometheus follows a pull-based architecture where it scrapes metrics from monitored targets, while Sysdig uses an agent that collects data directly from the kernel and containers, providing more detailed system visibility.

2. Data Collection: Prometheus focuses on monitoring and alerting using its Prometheus Query Language (PromQL), while Sysdig offers capabilities for troubleshooting, security, and forensics through its Sysdig Secure and Sysdig Monitor products.

3. Scalability: Prometheus is more suitable for small to medium-sized deployments due to its limitations in terms of scalability and storage capabilities, whereas Sysdig is designed for larger and more complex environments with advanced performance features.

4. Open Source vs. Commercial: Prometheus is open-source software maintained by the Cloud Native Computing Foundation, while Sysdig provides a mix of open-source tools and enterprise-level solutions with additional features and support available through its commercial offerings.

5. Integration with Kubernetes: Prometheus is widely used for monitoring Kubernetes clusters with native support, while Sysdig offers extended capabilities for container-level monitoring, alerting, and security in Kubernetes environments.

6. User Interface: Prometheus provides a basic web interface for querying metrics and creating simple dashboards, whereas Sysdig offers a more intuitive user interface with advanced visualization tools, dependency mapping, and integrated troubleshooting capabilities.

In Summary, Prometheus and Sysdig have key differences in architecture, data collection methods, scalability, open-source/commercial offerings, Kubernetes integration, and user interface functionality.