you will make a blog only for earning money from AdSense? Mfa Site Blog about Religion - that God Google will forgive you
I think trying to blog around a topic soley to make money wouldn't work out well. I'd imagine that having no interest in the topic would bore you to the point that after 2-3 weeks and not a lot of traffic you'd give up. Blog about something you know that's interesting and other people will find interesting where you can lend your expertise and provide unique content not found anywhere else on the web.
Time and time again people want "high paying" topics. Well, you wont get very far with it as you will lose passion. Blog about something you are interested in!