It depends on what you are looking for, as they each have their pros and cons.
Spring.NET is the most mature as it comes out of Spring from the Java world. Spring has a very rich set of framework libraries that extend it to support Web, Windows, etc.Castle Windsor is one of the most widely used in the .NET platform and has the largest ecosystem, is highly configurable / extensible, has custom lifetime management, AOP support, has inherent NHibernate support and is an all around awesome container. Windsor is part of an entire stack which includes Monorail, Active Record, etc. NHibernate itself builds on top of Windsor.Structure Map has very rich and fine grained configuration through an internal DSL.Autofac is an IoC container of the new age with all of it's inherent functional programming support. It also takes a different approach on managing lifetime than the others. Autofac is still very new, but it pushes the bar on what is possible with IoC.Ninject I have heard is more bare bones with a less is more approach (heard not experienced).- The biggest discriminator of
Unity is: it's from and supported by Microsoft (p&p). Unity has very good performance, and great documentation. It is also highly configurable. It doesn't have all the bells and whistles of say Castle / Structure Map.
So in summary, it really depends on what is important to you. I would agree with others on going and evaluating and seeing which one fits. The nice thing is you have a nice selection of donuts rather than just having to have a jelly one.
