They don’t make this easy, do they? Well, here I go with another multi-part answer.
I have read every Harry Potter book an average of 7 times. Maybe more. I haven’t counted, but it’s a lot. Regardless, I cannot say this makes it my “favorite” series. Yes, I love them, and–clearly–I enjoy reliving the magic of Hogwarts with Harry, Ron, and Hermione at least once a year. But I tend to see it as a palate cleanser, or, “cortex cleanser”, if you will. When I’m feeling particularly wound up or just want something light and enjoyable, I pick up Harry Potter. It doesn’t matter which, I just grab the first one I can find and go. When I’m done, I’m ready to start something deeper, or more “hard-hitting”.
Then there’s a series like, say, Wheel of Time, which I would love to reread, but can’t seem to find time to set aside for 14 books, all of which consisting of at least 800 pages. At least. Not to mention the interweaving story lines making it more like 5 series wrapped up into one, giant epic. Again, not my favorite, but a contender.
I would have to say my favorite series is the Ender Saga. Specifically, the four books following Ender himself: Ender’s Game, Speaker for the Dead, Xenocide, and Children of the Mind. I may not have devoted as much time to them as I have Wheel of Time, and maybe I don’t reread them every year like Harry Potter, but these books make you think. Not just about the future they propose, but about the present in which we currently live. Orson Scott Card teaches his audience about politics, strategy (military or otherwise), and philosophy. It isn’t pedantic or condescending, but you resurface from the pages with an enlightened state of mind. I may sound crazy in saying this, but I felt as though I was more perceptive after reading them. It seemed–to me, at least–I thought things through more thoroughly and analyzed matters with greater aplomb. I used words like “aplomb” with greater aplomb.
Within all that learning stuff, I also discovered a fascinating story. Card makes his futuristic version of Earth and its colonies such a realistic possibility. Kid geniuses, alien life, space battles; it is crafted so deftly that nothing seems out of place or far-fetched. Even at the story’s most implausible points, he has you thinking, “Well of course there are pig-like humanoids on another planet who are technologically undeveloped yet linguistically gifted, where else would they be!” Thus is the mark of a fine piece of science fiction; it coaxes the reader into suspending their disbelief without realizing much of it is ”unbelievable”. Great writers of any fiction genre build their own realities this way, and I would certainly count Card among them.
Within each of these series (and many not listed) are individual books which I would consider some of my favorites; however, as a whole, Ender will hold the series title until I discover one that deserves it more.
Here are a few series I did not name, but highly recommend:
His Dark Materials, by Philip Pullman
Divergent, by Veronica Roth (3rd and final installment, Allegiant, to be released October 22, 2013)
Vampire Academy, by Richelle Mead (NOTE: The title/cover art for this series are terrible representations of how good these books really are, I swear!)