I've never been particularly into class lore because I don't feel "class lore" in itself has much depth, I just like lore in general. I know alot of people got super interested in Tirion Fordring, Varian Wrynn, or Alexandros Mograine. Mograine is actually sorta interesting, but otherwise I never understood the allure of these characters - especially Varian.
If I had to choose one, probably Warlocks...because of WC3.