Well, my favorite author is Tamora Pierce, and I pretty much love all her books. But for individual favorites, I would have to say... there's so many to choose from...
1. Homeless Bird
2. The Blue Sword
3. The Linnets and the Valerians
I don't know any of the authors, and they're all older books. The Linnets and the Valerians could be very old, as I found it in a box in my grandmothers attic. These books are some of the collection that I've had for as long as I can remember, and I would never get rid of them.
And of course, no fantasy author can beat the likes of JRR Tolkien, or CS Lewis, etc.
Edit: So, it looks like the Linnets was written in 1962, and I'm pretty sure I have a first edition. Cool. It's a wonderful book, especially if you like a little witchcraft in your life.