I really like lore and have had a lot of free time over the past Spring/Summer so I've read them all. The war of the Ancients were my favorites. It was more interesting reading an actual story that was based on only a few bits of history instead of reading recounts of what happened in the games. I especially liked seeing a happy laughing Malygos in the story. I also liked The Last Guardian because I think Medivh is an interesting character in WoW's history.

There's also a new book that just came out not mentioned on your list.