I find Darkness boring. It takes too long to kill the mobs. Deception seems better for leveling although I probably spend way more time "seething" in Deception.
Respecs are cheap. Try em both
trying them both is good advice . I would wait and go darkness at 30+ . I switched to darkness when i got ashara . I dont really notice mobs taking longer to die , if its does take longer then its a tiny amount.
the talent were darkness comes into its own is the one that makes lighning do 75% more damage and heals you after getting 3 buffs from shock. Golds dont get close to killing you when you use that.