Coldline Storage is the most suitable option for backup files in a disaster recovery scenario due to its cost-efficiency for rarely accessed data. It offers lower at-rest storage costs with higher latency and lower availability, which are acceptable trade-offs for disaster recovery backups. Multi-Regional and Regional Storage are designed for frequently accessed data, making them less cost-effective for this use case. Nearline Storage is better suited for data accessed once or twice a month, not for rarely accessed backups. Archive Storage would be ideal but wasn't listed as an option, making Coldline the next best choice according to Google's recommendations.