The most important thing to think about when considering how best to use your time on the internet is what your interests are.

Do you like playing games when you're online? There is a way to get paid for that.
Do you like online shopping? You can make money doing that too.
Social networking? There's money there.

You can find ways to make money and/or earn rewards and free stuff doing just about anything that you are already doing online. The hard part is finding the best sites to help you do that.

Just remember: your time is valuable. Don't do anything for nothing.