I'd recommend SQL Server Express or other database.
- It's free.
- It integrates very well with C#, including LINQ.
- It's faster than a homemade solution.
- It's more reliable than a homemade solution.
- It's way more powerful than a simple disk-based data structure, so it'll be easy to do more in the future.
- SQL is an industry standard, so other developers will understand your program more easily, and you'll have a skill that is useful in the future.
