[kellros]

From a technical viewpoint it all comes down to the CAP theorem and what is priority: http://en.wikipedia.org/wiki/CAP_theorem

Not mentioning all the other factors that are involved in choosing a database (ex. current staff skills, who will be maintaining the project if you decide on x but everyone uses y, what licenses do you already have etc.), you should consider the CAP theorem when choosing between a RDBMS, NewSQL, document based, graph based, key-value or file based storage.

Each database was designed to solve a specific problem, even though most databases are advanced enough for general use cases (ex. you can use a RDBMS in a similar fashion to a key-value store).

I'd say unless you have tried out what's available, it's going to be hard to make a choice - so get started!