Oh yes, I love The Last Battle, it is awesome... and I will commit non-sycophanty by saying that, no I don't think Knife is better than The Last Battle, sorry.
(still totally squee-worthy for the nom, yes!)

I haven't actually thought about which Narnia book is the best. The Silver Chair and The Last Battle are probably the deepest two, yes. My favourite bits in Prince Caspian are the whole Lucy-sees-Aslan thing, but the structure of the book isn't so good. And the follow-the-signs thing in Silver Chair is a similar stricture as the Lucy-sees-Aslan thing in Prince Caspian, anyway. Voyage of the Dawn Treader was the most fun, I think. We got Eustace and Reepicheep!
Well, they're all wonderful, anyway.