https://api.unrealengine.com/INT/API/Runtime/UMG/Blueprint/UUserWidget/GetIsVisible/index.html
Which method should I use? Which is preferred? Thanks.
According to the source, IsVisible returns whether the current widget is visible or not. This could mean any widget, like for instance a button within a menu, or a text field within a dialogue window. The latter, GetIsVisible only seems to return whether the widget in its entirety has been added to the viewport or not (for instance, when you add UI for display in-game). In fact, the code mentions that this function is now deprecated and that people should use IsInViewport() instead. Epic probably realized the naming was confusing.