All the information I have ever seen says that you should start with a niche you are passionate about. The reason is you have the knowledge about the subject and your passion should show in your writing.
I write about so many topics as I have great difficulty concentrating on one thing....I get bored really easily.
I am writing around 17 blogs at present on Blogger.com about different subjects, 3 with adult content. You know what they say...sex sells!.
Obviously I write on Hub Pages but I have been experimenting with Wikinut. They are somewhat similar to HP and you start to get paid as soon as you start publishing. I have earned only a small amount in a couple of weeks but it is starting to rise steadily.
My Blogger sites are monetised with adsense and they are getting a few clicks also.
You will hear it time and time again that it is the work you put in now that will pay you back in the future. We all want instant gratification. My advice is to hang in there and follow a mentor who has walked the walk.
I am sure you will find the person you are looking for here on HP.
Try to do it on your own and you will find it both time consuming and very lonely.
Hope this has helped in some small way.
Take a look at Wikinut
My Blogs are here in one place on Networked Blogs
Let me know what you think