John Regan

This plugin adds a simple button to the post editor screen which allows editors to duplicate posts quickly and easily. It’s so simple that no configuration is necessary!
Features
<ul>
<li>Copies with just one click!</li>
<li>Make duplicates from the List or Edit Post view</li>
<li>No configuration needed</li>
<li>Works for all Post Types</li>
<li>Integrates seamlessly with the WordPress UI</li>
<li>Extremely lightweight (~8KB)</li>
<li>Thorough Documentation</li>
</ul>

Simple Copy Post Button

Copies/Duplicates Posts, Pages, and Custom Post Types with just one click.

Manoj

For creating a copy of posts and pages while retaining all the styling, content, title, meta info and taxonomies.
<ol>
<li>
In Posts/Pages screen, you can click on ‘Copy As New Draft’ link below the post/page title: this will immediately create a copy and return to the page.
</li>
<li>
In Posts/Pages screen, you can click on ‘Edit As New Draft’ link below the post/page title: this will create a copy and redirect to edit the page.
</li>
<li>
In Edit Posts/Edit Pages screen, you can click on ‘Edit As New Draft’ link above ‘Publish’ button: this will create a copy and redirect to edit the page.
</li>
</ol>
Please Note: No any kind of settings needed.

Simple Copy Post Button vs AMS Post And Page Duplicator