When to use MongoDB over couchDB?
MongoDB provides:
Availability and Partition Tolerance and eventual consistency.
Supports dynamic queries. It can be used when your data changes frequently.
Master-Slave Replication.
CouchDB provides:
Availability and Partition Tolerance and eventual consistency.
It can be used when you have occasionally changing data. Places where versioning is important.
Master-Master Replication.
Hope this helps 