Cacao beans are whole, raw beans. Cacao nibs are cacao beans that have been cut into edible pieces. Cacao powder is made by defattening (removing the fats from) cacao beans. So cacao nibs are a whole food and cacao powder is a processed food. Which one is healthy?

Cacao powder? Even though cacao powder is a processed food, it is actually health promoting: see Cacao Powder for details. For example, in the article Cacao, Dr Greger explains:

Cacao nibs? The concern is their high saturated fat content. So consuming them in large amounts is discouraged by Dr Greger. At the same time, he's okay using them in small quantities as garnishings on cake, for example. See Berry Chocolate Chia Pudding recipe at NutritionFacts website — cacao nibs are listed as an optional garnishing.

At offset 16:15 of this Q&A video, Dr Greger explains: