Which supplier should control the default slot on digital devices? We analyze alternative ways to assign the default position for digital goods like search engines. First, we show that competitive bidding for the default usually rewards the higher-quality incumbent, yet it can reduce consumer welfare by cranking up ads and data extraction. Second, and perhaps surprisingly, giving the challenger a regulatory slice of defaults dulls rivalry and raises both firms’ profits while harming consumers. Third, “choice screens” boost short-run consumer...