Pick the lowest dip I can find say, this week, and invest all my principle. Or, dollar cost average anyway....if so, over what time horizon? Surely not over the next year. Maybe a week? A month?
Both can work. You need to distinguish your situation and which is strategy that you're comfortable with. We have different situations and one can invest with the DCA strategy because he's comfortable with that while the other, he's just going to wait for the dip and buy at his picked price as the dip but you might find it hard to see if it's the actual dip on this cycle.