For those older readers of Narnia, here are some of my own thoughts on which order to read the Chronicles. For those new to Narnia, you may be unaware that there are two orders of reading the series; one, chronologically by publication order, and the other by Narnia's internal chronological progression. The first is is numbered as thus: THE LION, THE WITCH, & THE WARDOBE, PRINCE CASPIAN, VOYAGE OF THE DAWN TREADER, THE SILVER CHAIR, THE HORSE AND HIS BOY, THE MAGICIAN'S NEPHEW, and THE LAST BATTLE. With this omnibus edition of Narnia, one of fantasy's most popular series has, of course, been ordered as Narnia is now published, with MN as the opening book and LAST BATTLE as the ending book.
With two publication orders of Narnia, many people question which to read. For several reasons, I recommend the first publication order to be read first, the internal chronology second..
If one reads the history of Narnia as strictly that, one is much more likely to lose the truths Lewis was trying to impart. When one reads The Lion, if they had not read Magician's Nephew, they will be unaware of where the Lamp-Post came. Lion is essential a story about Edmond coming into the salvation of God. It creates a real sense of wonder, a wonder that would be diluted with knowledge of its creation. It's a mystery, an account. You become less concerned with the book in context of the whole series, and more concerned with the book in context of the book. Some things you might miss or not pay much attention to because you have already taken into account in context of the story's chronology, and not examined what Lewis was trying to say through this. Also, you get to follow the characters throughout the books, which is lost in the new order. The four Pevensies are in Books I and II, then only the two younger are in III, along with a new character, a cousin named Eustace. Then They can no longer go on, and Eustace and Jill Pole is in Book IV. This is lost in the new order. Also, you can see Lewis's growth as a writer, getting more and more realistic in characterization as each book was written. Of course, when he was writing these he was already a phenomenal writer: but this provided room for more growth, and he developed his already great gift even more so.
Also, as Paul Ford points out in his excellent Companion to Narnia, the old order is reflective of Biblical history. God's people are in bondage to the Egyptians, and he frees them. But the wine and groan, and in the end many die in the wilderness. Then they go into Babylon, and hear all these creation stories. After this, they go and record their own history. Lewis, after trying to write a creation story, found he could not, and went on telling other stories of Narnia. Only after coming more and more into the spirit of the series, after a good deal of history had been written, could he go back and finish Magician. To quote the preface, Ford says the original order allows "the reader to experience something experience something truer than even Lewis intended: the primordial necessity of passing first thru redemption, then into a reinterpretation of one's own story, and finally allowing the future to take its providence course". And how true that is. How many times can one understand what God is doing in your life until you come to know him? When you come to the salvation and knowledge of Christ, after some time elapses you can go back and examine your life, and can see where God's hand was on you, guiding you to that place where you met Christ. And in so doing, you come to trust God in a deeper sense, and as he took care of your past, he will also take care of your future. Of course, this was not intentional on Lewis's part, but it shows when God gives someone a gift, that person can reach people in such a way as to be totally beyond the person, and directly pointing to God. This aspect truly points to Jesus Christ and the "great Emperor Beyond the Sea,".
Of course, there is a balance. They are stories, and should be enjoyed as such. Through these stories, Lewis gives children and adults alike truth. However, if you overanalyze them, you are losing the spirit of the series. One must first enjoy them as stories, and not go dissecting them without reading them simply for stories. That is why the chronological order also has its merits. Ironically, however, it is better balanced to read it in original order for reasons cited above, also because you can take each story on its own, appreciating both the story and the symbolism. Without the interconnecting theme of history behind it, you are forced to look more at what the story is and what it is saying as to what the Chronicles is saying as a whole. That is one side. That is not balanced. Then, go back and read the stories in chronological order. That makes you appreciate the series as a whole.
In conclusion, each has its merits, and without each it they are not balanced. But for first time readers, read it in the original order. You will get more out of it. That is the most balanced way to read and appreciate the stories. Afterward, go back and read in chronological order. Then you will have a balanced and complete view of Lewis's fabulous and God-given Chronicles of Narnia.