I'd definitely recommend Couchbase, I feel it's a more robust and feature complete NoSQL document store for most use cases. It's easier to set up, and write performance is much higher than MongoDB in most configurations due to the master-master architecture. The N1QL query language is the most robust NoSQL query language out there, and it's SQL based so very easy to use. Additionally, in the last year, Couchbase has added a complete Full-Text Search system as well as Analytics, which is SQL-based MPP analytics querying with no ETL (think built-in Hive/Hadoop on JSON documents).
