By the title, I don't mean whether it's boring or interesting for the reader. Writing all day, every damn day makes you appreciate when a topic is just interesting enough to keep you from throwing things to keep yourself awake but not interesting enough to make you freak out. Why would something interesting be bad? Perhaps an explanation is in order...
I have ghostwritten a number of boring topics. If I told you the topics, just listed them, they would bore you. Now imagine writing on topics like that for hours when you know that Charmed may possibly be on or maybe there's still a Cadbury egg in the pantry that you missed. It's rough.
So, an interesting topic should be a lot better, right? Not remotely. A too-interesting topic can keep you researching way past the point that you should. That makes the writing process go on and on and on. This means less money, fewer opportunities for new projects and glaring spouses. I first noticed the glare this evening when I showed him the third giant insect native to a specific African jungle. I was already half an hour past the information I needed and was still going. That's what an interesting topic can do.
The ideal topic is one that is interesting, but not fascinating. It's easy to research, but the Internet isn't crammed full of information about it. And lastly, there should never be too damn many pictures of it.