MongoDB and Couchbase are two popular NoSQL database systems that have evolved their replication solutions to address the growing need for highly available, scalable, and globally distributed deployments. MongoDB's replication architecture is based on a replica set, where each secondary copies data from the primary asynchronously, but can become a single point of failure if not managed properly. In contrast, Couchbase follows a peer-to-peer architecture, allowing multiple independent clusters to be created and replicated across different geographies. This provides flexible topology, workload isolation, and heterogeneous scaling benefits. Both systems offer cloud deployments with MongoDB's Global Cluster and Couchbase's cross-datacenter replication solution, which support true active-active setups for concurrent writes across multiple regions. While MongoDB's setup can become complicated as it scales, Couchbase's deployment is considered more intuitive and easier to manage. Additionally, Couchbase offers advanced filtering to replicate subsets of data and prioritizes ongoing replication compared to new replication or vice versa.