What are the key factors to consider when choosing a BGP transit provider?

The key factors are network performance, redundancy, peering policy, DDoS mitigation, and support SLAs. Performance hinges on their global route optimization and latency to your users; request looking-glass servers to test routes. Redundancy requires multiple upstreams within their network and diverse PoP locations. Their peering policy (open or restrictive) directly impacts your cost and performance - seek extensive peering at major exchanges like AMS-IX. DDoS mitigation should be a core, integrated service with clear thresholds and response procedures, not an expensive add-on. Support SLAs must guarantee rapid response for routing issues, not just circuit outages. Before committing, verify their route announcements and filtering practices.