Google likes fresh content, so do your readers. So why duplicate.
Duplication could be for some genuine reasons such as:
1. Replication to split traffic between two sites
2. Replication to monetize on traffic from different geographical locations
3. Distribution of content on multiple sites for a varied target audience or markets
4. Viral marketing or allowing republishing for a [...]

There are free resources and then there are free resources for submitting your articles, but it makes sense to submit posts to websites with ranking equal or higher than yours.
Here is a list of websites with a page rank of 6 or higher where you can submit [...]