I have used Oracle, MySQL, and Mongo in prod situations. I have looked at Cassandra for evaluating it for potential usage in prod.
I can imagine situations where I could recommend any of the above. For example, if you are large financial company with billions of rows, I would go with Oracle. If you have smarts but not money and didn't need somebody to sue if something went wrong, then maybe Postgres would do . If I were a simple web based app with simple form submits, I would go with MySQL. If I had complex unpredictable data blobs and unpredictable needs to do certain types of queries against the data, I might recommend Mongo. If I have large amounts of data on which I want to do analytics I would use Cassandra.
Cassandra wins when you have a lot of data and not a lot of complex real time queries against it. It is especially good at scaling up on cheap data storage (think 100s of terabytes). It also has an unreal "write" throughput (important for certain types of analytics which write out complex intermediate results) though that is not relevant for the case described.
The problem generally with noSql solutions is that they increase the amount of storage to store the equivalent amount of information. You are essentially redundantly storing schema design with each "record" that you store. This really matters more than some might suspect, because when you can put an entire collection into memory, the read performance is much higher. You usually need 1/5th to 1/10th as much RAM to do the job with a traditional relational database (especially since MySQL and their brethren handle getting in and out memory better than mongo). This isn't so much the case for Cassandra because of its distributed storage nature, but it really isn't usable for real time transactions.
My recommendation, use a traditional database -- if in a Microsoft shop use SQL Server, otherwise I like postgres or mysql. If however, you have complex data storage needs that a noSql solution is perfect for, then I would go with that. If you are into back end analytics, copy the data as it comes in and put into a Cassandra (or one of its similar brethren) as well.