I'd be careful (very, very careful) with the words "of all the time", but I take it that you had in mind only current (or more or less current) books from current authors. But I won't be underrating them as well, because although I'm not sure if the discussion can be of the same quality
I believe there are lots and lots of people who don't mind discussing anything from Harry Potter through Narnia and Conan to the works of H.P. Lovecraft. I am sure LotR is number one among these and only time will show whether for example Harry Potter is going to fall into nothing, but generally all the six million volume fantasy sagas definitely provide us with far much larger universe than LotR, with for example great possibilities for fan fiction etc. So why are they not the number one? Basically, they often lack the other things that Tolkien can offer: the language, the "vividness" (or how to say that) of the world, the complexity of the characters, who knows what else? And also the way how it's all put together. Other books that have this may lack for example the complexity of the world in which the stories take place. And so on.