Warlock Wow Classic
Another option for leveling on a PvP server might be DS/Ruin. Big survivability and nice damage, overall average.
Ah hell no, it's shit for leveling and you don't have enough +Shadow damage items to make it worth it while leveling. Doesn't hold a candle to imp. Corruption, imp. Drain Soul, extended range for your spells, a slow and instant SBs once in a while.