I have found so far that any of my hubs about making money...especially earning money online, has been popular. Also, health-related hubs seem to do very well. These are the main topics I've seen do well in my own hubs.
However, I've read hubs about art, DIY and how-to's that were excellent and I bet they did super!
I think that if you put your best into any hub, you will see results, anyway. But try scanning the topics for hubs with lots of comments or find writers with large followings and see what they're writing about.