Kazzak for Horde PvP, Draenor for Horde PvE.
Why anyone would want to play on a PvP realm these days is beyond me. Whenever I cross-realmed to a PvP server the Timeless Isle was just impossible.
Those are the best times, probably my two fondest wow memories are Southshore battles and the isle of gank (Isle of quel danas for newer players) where works fights were huge and really fun. Best for me was isle of
Gank where huge battles would brake out over control of the cliff path to the sunwell dungeon. No insta dungeon porting then so you had to fight up a cliff to gain control of the dungeon. My Boomkin mass pushback was amusingly effective on defence
Pvp servers add an edge of fun for me, though each to their own.