I hope you will find your answer here http://hshno.de/H18Y2nPde

What's your current data size? How much do you think it would grow over a period of next 5 years?

NoSQL is not a panacea. It has it's own pros and cons. Can you forsake consistency over availability or vice-versa? Understand CAP guarantees (https://en.wikipedia.org/wiki/CAP_theorem) and the trade offs that you can make, before making the decision of migrating to NoSQL.

Ok, here's the comparison of Mongo and CouchDB.

Mongo:

• JSON based document store(BSON actually when it's stored in the file system!)
• Sharding, Journalling and Replication(Master/Slave) support
• Different storage engines(MMap, WireTiger etc.) for different use cases(Is your system write heavy or read heavy)
• 16MB is the max size limit per document, use GridFS if you're planning to store huge files
• Javascript based querying
• No joins or transactional support, you can still perform atomic operations
• Tuneable consistency through settings like Read Preference, Write Concern
• Text and geo-spatial search features
• It does support Map/Reduce type of queries
• CP system from CAP standpoint

CouchDB:

• Again, document store, but store the data in custom binary format
• Multi-master replication
• MVCC system, hence offers ACID semantics
• AP system from CAP standpoint

Hope this helps!