Another problem with free blog sites is that you are not totally in control of your blog. I have a friend whose blog was taken down because of some issues. Yes, free blog sites can delete or take down your blog if they think there is some kind of violation to their policies.
If you are looking into long-term income generation, free blog sites may not be a good option.
I think before you venture into blogging, you have to assess first what you want and how you want to accomplish it. Whatever you decide, make the most out of it. And most importantly, enjoy what you are doing!