Recently, I have looked around for a good NoSQL database for my new project. I have been using MSSQL for a while but there seems to be more and more complexity as the data models are no longer table-compatible with sub-items and array and a volatile schema.
I have considered DocumentDB on Microsoft Azure on its very interesting indexing capability and the fully managed environment of Azure. However the current price is too expensive for me: 20 USD/month/collection. Some people suggested to put every type into a collection and use a field to distinguish them, but I feel that it is quite messy, especially for NoSQL starter like me. So I went back to some other popular choices such as RavenDB and MongoDB. RavenDB seemed to be a great fit at first as it seems to have very good interface for .NET (C# is my language of choice at the moment) and an awesome web interface, but I then realized that the free version actually has a lot of limit, and I did not plan to incur too much cost on this project.
So I decided to go with MongoDB, which is hugely popular NoSQL database, and seemed to be totally free for my need.