Yahoo is a holding company focused on large, category-leading sites in Asian markets. They also own a struggling portal in the US.
Ha! Like the old joke that McDonald's is a real estate company that sells hamburgers.
They've made it clear that they're in the business of being a media company, not a technology company. So I would say that the media-focussed products like Tumblr are probably more reliable bets, but it also means that they're more likely to pivot based on unpredictable trends, rather than focus on any specific technological capability.