Shadow is quicker and you can multi dot and never die or have down time.

However near 116+ it slows down and sucks at 120 until you get gear. Once your geared and know the spec (With the right essences you can do big aoe burst and single target) but without CDs your AOE will never be that great if your playing with other decent people.

Just stay shadow for leveling. Max range multi dot. Run to next mob and repeat.