World PvP: Raw uninhibited pvp with many factors at play.
Dueling: No better way to learn classes and their weaknesses / strengths than this.
BG: till you want to rip your eyes out. Learn that being a "Hero" isn't always the best way to win.
Arena: Nothing makes you focus harder than this group-up.
Live streams: You can pick-up quite the tips and tricks from some of the top players in the world. This is basically like your research portion of PvP, .