Neither Castle.Windsor or Spring.NET are new.
- Castle Windsor have been around since late 2004
- Spring.NET have been around since early 2006
They are two comparable DI Containers that essentially aim at providing the same services, so you don't need to learn one before the other, and neither do you need to consult any kind of specification on when to use which one.
I've been using Castle Windsor for about half a year and am generally happy with it. Spring.NET I have yet to look at, but it looks like it is very closely tied to the configuration system and doesn't support programmatic registration, and if this is true, that would be a major drawback in my eyes.
Castle Windsor and Spring.NET are not the only DI Containers available for .NET. Here's a larger list:
- Castle Windsor
- Spring.NET
- StructureMap
- Unity
- Ninject
- autofac