What is the "best" plugin for Google Retargeting?

Looking for a simple way on how to activate "Retargeting" for shop products.
Once a visitor has studied a certain webpage/product and leaves this page without conversion/purchase, a banner should follow him on certain other websites.

This link and this Google search  might be of help

I found that it was extremely simple to integrate google remarketing into my site by simply adding the additional lines of javascript into my existing google analytics plugin configuration:
example:

top section:

    (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
    })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
    ga('create', '{GOOGLEID}', 'auto');

var google_conversion_id = xxxxxxxx111111;
var google_custom_params = window.google_tag_params;
var google_remarketing_only = true;

and in the next section:

ga('send', 'pageview');

/* <![CDATA[ */
var google_conversion_id = xxxxxxxx111111;
var google_conversion_language = "en_US";
var google_conversion_format = "1";
var google_conversion_color = "ffffff";
var google_conversion_label = "dfhwre56wsgf4";
var google_conversion_value = {TOTAL};
var google_conversion_currency = "USD";
var google_remarketing_only = false;
/* ]]> */