WOTLK is still no. 1 for me except what they did with Arthas at the end, Warlords could be my number 2 instead of pre-BC, but that's because it's hard to fuck up Warcraft 1/2 lore with all the background writing they already have for it from the first 2 games and subsequent books.
Cata and BC had a lot of interesting things happening (Dwarf wedding in Twilight Highlands
, Outpost 15 defense in Blade's Edge
) , then there's the current expansion and its 50% china copy paste 50% strained attempts at linking pandaria to the rest of Azeroth, and a lot of stupid names like NZoth and Chi Chi zzzz.