Booking Through Thursday - Categories

Booking Through Thursday is a fun weekly meme that's usually about books or reading in various ways. I don't participate every week, but I do try to most of the time. This week is one of the ones I'm going to answer:

Of the books you own, what’s the biggest category/genre?
Is this also the category that you actually read the most?

My book collection is actually split in two for the most part, and to be honest, I'm not sure which is the bigger: There's the science fiction and fantasy side of things, which is also the section I tend to revisit the most: Tolkien (these could almost be considered their own section as proven by the Tolkien collection list post, and the fact that a lot of the books are about Tolkien and his works), Mercedes Lackey, L.E. Modesitt, Elizabeth Moon, Jo Graham etc.

The other section may actually be bigger though: Non fiction history books - the more academic the better: These are mostly split between books about the Classical World (Romans and Greek), and those about the Medieval World, although there are a few on Egypt, mythology and the like as well. A lot of these are a legacy of a BA degree in history, but I keep adding to the collection as well. Thing is, I buy the books, but I don't seem to read them that often. Possibly because for these books I feel like I need to have a pencil and paper out at the same time. Despite not reading the history books, I'm always on the lookout for a new book to add to the collection for some funny reason.

I really don't know which book category is the bigger.