It can sounds a little bit clichê, but for me the best fantasy book series is still the one concerning all the Tolkien's LotR universe: Silmarillion, The Hobbit, The Lord of the Rings, The Children of Húrin, Unfinished Tales (I guess that's the title in english). Yes, the LotR books (1,2,3) can be a little boring sometimes, I agree, specially the chapters of Frodo and Sam walking on the mountains.

Martin is doing a great job with the books (and HBO with the TV serie), and takes the 2nd place.