Functions & Logic Apps are two distinct offerings by Microsoft Azure. I wonder what are the use cases that one should favor the new Functions offering over Logic Apps.
Azure Functions is code being triggered by an event.
Logic Apps is a workflow triggered by an event.
That means that they are also, in fact, complementary. You can, as of sometime yesterday, add a Function as part of a workflow inside a Logic App via the Logic Apps UX.
TL;DR - It's Logic Apps + Functions, not Logic Apps OR Functions.