allilevine

This plugin adds an options page (Settings > Login Screen) that allows you to customize the WordPress Login Screen (wp-login.php). You can:
<ul>
<li>Upload a custom logo (it will be resized to fit if necessary)</li>
<li>Choose a link color</li>
<li>Choose a link rollover color (defaults to a darker shade of the link color)</li>
<li>Choose a button color (defaults to a button version of the link color)</li>
</ul>
The plugin also links the new logo to your site URL.

Simple Login Screen Customizer

Good

Choose a logo and link color for the login screen.  The plugin will do the rest.

diablue

Plugin allows admin to upload custom logo for WordPress login page.
After activating the plugin, follow these steps:
<ol>
<li>Go to Settings -> Custom Login Logo</li>
<li>Click “Choose Image”</li>
<li>Select or upload your logo</li>
<li>Click Save Changes</li>
<li>Refresh the login page to see the new logo</li>
</ol>

Diablue Login Customizer

Easily add a custom logo to your WordPress login page using the built-in media uploader. Change WordPress login logo from admin panel.

Simple Login Screen Customizer vs Diablue Login Customizer