I usually go Chalice > Sorc's > Deathcap > Grail.
The extra raw burst goes perfectly well with some surprise roaming and in mid-game skirmishes.
EDIT: And to the ones saying more sield, Lux's shield has a total scaling of 0.7, so it also gets the benefits of extra AP.
It's basically a personal preference of Burst over DPS/more cc or the other way around.