I know this is an old question, but here are my thoughts:
I personally like Ninject. I like the fluent interfaces and avoiding of XML. I generally like XML, just not for this kind of config stuff. Especially when refactoring is involved the fluent interfaces make it easier to correct.
I miss StructureMap's ObjectFactory, but there are easy workarounds to add that to Ninject.
As Jeffery points out you don't have to use the [Inject] attribute when you only have one constructor.
I found that I prefer the fluent interfaces not only because they avoid XML, but because they cause compile time errors when I change something that affected them. The XML configuration doesn't and the less I have to remember to change the better off I am.
