Speed of leveling was the fastest for me with a Fire/Dark Corruptor.
At level 10 I would be running at -1 x 8 solo.
Powers:
Super speed, tar patch, Darkest night, FireBlast, Fire Ball, Rain Of Fire
Zip forward, herd a group with Darkest Night and drop tar patch on a corner - rain of fire and fireball until well done.
By 22 I would be at +1 x 8 - solo.
Super speed, tar patch, Darkest night, FireBlast, Fire Ball, Rain Of Fire, Aim, Firebreath, Howling Twilight, Shadow Fall, Fearsome stare.
Zip forward, herd a group with Darkest Night and tar patch a corner - fearsome stare, Howling Twilight and then Fireball, Fire Breath and rain of fire.
By level 50 once I had some IO's in I was soloing +4 x 8. I would herd the Wall in Cimerora timing it so the patrols would come by at the same time thus getting more than the aggro cap. This was my go to IO farmer on the wall.