Upload & Sell: Off
As you may well be aware, nothing will be pure white unless it's lit properly. And, conversely, anything can be pure white if it's lit properly.
That being said, if you're going for the whitest white with the least effort, #66 is absolutely chock full of brighteners and will be a little easier to work with (as far as being white, anyway). Its brightness can be a liability with regard to spilling back, though.