For my tastes, it's not a matter of the biggest scope or the most obsessively detailed world history.
What I appreciate about Tolkien's world is the sense of wonder I felt when reading LOTR. He explained soo many details of that world but just as crucially he was very artful about what he chose not to explain. Adding to that, Tolkien and the characters themselves seemed to share this sense of wonder. Gandalf, who knew more about the world than even the Elves, never lost his sense of wonder and reverence for things.
GRRM's fantasy world is, well... more realistic, that's for sure. Characters are mostly just trying to be king, or to fuck, or get money, or simply survive. I like those books too. And GRRM has said of course that he was explicitly trying to create something like an anti-LOTR that showed the lives of people who weren't necessarily heroes or even good people.
I like the GRRM novels but I still prefer LOTR's sense of wonder. But, nobody's wrong if they have the opposite opinion. Or if they hate both. :)
