If the question is what is my favorite topic to write about I would probably have to say cleaning and organizing. However, I'm so obsessive about the topic that I have spent forever planning my cleaning and organizing hubs that I haven't actually published them. I look forward to writing them, but I want to look over my binder, guides, books, etc - Okay, I'm a little obsessive about it.
As for what topic is the most successful or makes the most money it would probably be a how-to guide or something on technology. My biggest, highest rated and editor's choice hub is a how-to guide on technology, so I guess I combined the two. I think it's important to find a how-to technology topic that has not been well covered on the Internet though. This can be a challenge.
Hope this answers the question! ~Michele