As far as you need to be concerned as a .NET developer, you can freely interchange them as and when you feel like it.
Articles Written by Peter Shaw
You have a custom type, but you know nothing about that type, Learning to use ToString solves that problem.
Use code extensions to expand the core principles of code re-use.
Review using the XElement interface and discover one place where XML is still used that's potentially quite useful to you.
LINQ has a trick up its sleeve from .NET 4 onwards for dealing with large amounts of data and multiple CPUs. Learn to leverage LINQ.
There's no shortage of functionality built into the .NET framework to help you encrypt and secure your data. Follow along and feel more secure.