If you're going to pick a product based on how familiar with its implementation language you are, a whole lot more people can use Cassandra than Riak. :P But r

If you're going to pick a product based on how familiar with its implementation language you are, a whole lot more people can use Cassandra than Riak. :P But really you shouldn't care what language your database is written in, it won't affect you at all unless it's written in something esoteric enough that there's no way for your app to interface with it. (Cassandra's native api is Thrift, which means you can use it from damn near anything.)