LotR, we get the Silmarillion (Sp?) and
the Lost Tales (Vol. 1 & 2), and
the lay of Berlain (Sp?) and
the Hobbit, and
The Children of Hurin, and
the other one in that series..... oh, yeah, we also get the actual Lord of the Rings.
But, look at the sheer history and depth of Tolkien's world compared to Rowling's, it's just... amazing.
So, obviously, my vote was for LotR.
@Ray: Boring? LotR is anything but... unless you can't get out of the first book of the Fellowship.