SQL Server

SQL can be a very useful tool but it does add quite a bit of overhead to your application in terms of installation and configuration. It's one more thing that can break. In my experience, if you have a simple data structure that can easily be stored in the file system, then you should do that. If you can make your data human-readable (e.g. store in JSON format), then you can also have the added advantage of removing some debugging complications.

In my case, I have a simple flat file structure that can easily be parsed into in-memory data structures once my application is loaded. Further querying is accomplished in the code using LINQ.