I think you can EASILY compare the two worlds, as evidenced by the replies here. Then again, I can compare summer holidays to alligators.
For my money, it's Harry Potter's world. I find it more convincingly drawn, and the appeal of that world pervades the books. All the time I'm reading, I want to go there, and it makes the story all the more compelling.
I "liked" Narnia well enough, escpecially The Voyage of the Dawn Treader, but there's this thing… It's like, when you go see a movie with Tom Cruise in it, no matter what his character is doing, on one level, you're always thinking, 'It's Tom Cruise.' With the Narnia stories, whenever Aslan is in there, I'm always thinking, 'It's Jesus.' Yeah, he looks convincing with his golden mane and everything, but it's still always just Jesus. I find that alienating,