I hit this while reading some articles and found it is really helpful, one should check it before making any data store decisions.
To me there are several clear winners – redis/memcached for kv store, MongoDB for document store, and Oracle/MySQL for traditional RDBMS, and seems Oracle is a clear winner across corporations.
I believe what I decided to use memcached and then migrate to redis were both wise decisions, but I still doubt decided to use mongodb was a right decision or not. I will dig into MongoDB a little bit more to see if it got improved in the past two years for the issues I care, especially memory management mechanism.