Hubpages seems to have two trains of thought when it comes to topics. Some people say pick a niche and stick with it. This plan has merits because if you like to write book reviews you'll get people who will keep coming back to read the reviews because they are interested in that. But if you suddenly write a hub about baby clothes or christmas trees they're going to be turned off and not come back.
The second line of though is to write what you like, even if the subjects vary. This shows your readers that you have a wide range of interests and if they like your writing they will keep coming back to learn new things.
It doesn't matter which path you choose you just have to write good content. Ask yourself "Will someone be interested in this?" "How many people will be interested in this?" "How many other people have written about this?"
It's also best to write 3-4 hubs around a topic because that shows google you know what you're talking about and allows readers of that topic to jump from hub to hub and get useful information.