The Silver Chair was always my favourite, but my copy seems to have gone walkabout years ago, so I haven't reread it as an adult. I'm very fond of parts of The Dawn Treader too -- the world building, the lack of battles, Reepicheep, Eustace when he isn't being annoying.

The Susan bashing is mainly in the original but there's a fair amount of Problem of Susan fic that assumes she's in the wrong and needs to be fixed (by finding Jesus & living a life of unremitting charity work) before she's ready for NarniaPrimed. I've always thought Lewis was just plain wrong about Susan, at least insofar as the Narnian universe is meant to function as an allegory for Christianity, or even a coherent fantasy universe where Aslan isn't evil. But I don't think Lewis really understood adult women, or at least wasn't interested in writing them.