This was SUCH a hard decision mainly because LOTR, Narnia, Sword of Truth and Legend of Drizzt are ALL favorite fantasy series of mine, especially anything by Tolkien and Lewis. But when it comes to the series that is the most sprawling and epic, not to mention the series without which several others on this list would not exist (R.A. Salvatore quite being a lawyer so he could write fantasy just BECAUSE someone gave him a copy of LOTR in law school) I have to go with Lord of the Rings, but Narnia is a very close second.
Regarding George RR Martin; I don't enjoy his works nearly as much for the same reasons most people seem to love him. To be fair, I've only read the first book in the "Thrones" series, but to call an 850 page book a "fantasy novel" when maybe three pages out of all of them have anything close to actual fantasy going on robs the reader of his expectations. Of course more often than not I love having my expectations exceeded, but here the opposite was the case. To be honest it read more like historical medieval fiction, which is also fine, but it wasn't sold to me on that premise. When a book is called "fantasy" I expect a little more than just some unknown continent filled with douchey humans, a few dragon skulls and some large wolves. On top of that I found most (not all mind you, just most) of the characters to be thoroughly unlikeable. Yes flaws are very important in a character but at the same time said character should strive to and succeed in overcoming them; otherwise they're just boring assholes. With all of that being said I am still interested in checking out the series that premiers April 18th on HBO, mainly because I think the drawn-out elements of the novel will be better condensed and focused on screen. Also if someone wants to try to convince me that the series "does" get better in spite of my current issues with it I welcome your point of view. Then again I definitely prefer "high fantasy" in general so perhaps Game of Thrones simply isn't for me to begin with. Yet I generally love "Sword and Sorcery" (the opposite, right?) such as Conan The Barbarian as well. But if that's the fantasy sub-genre thrones falls under I think the problem I have with Thrones is that there's too much politicking, only a meager amount of swords, and almost no sorcery.
TLDR: I felt like Game of Thrones lied to me by calling itself "fantasy" and while I can understand it isn't "high fantasy," it barely even qualifies as "sword and sorcery" fantasy either, more like historical fiction. If you think it gets miles better after the first book please convince me.