Q: Bootstrap Row Builder - BS2, BS3 or both?

A: Please read on for some helpful tips on the Bootstrap version

First of all - the Bootstrap Row Builder Plugin merely adds the HTML markup to an article.
It does NOT add the Bootstrap CSS/JS files to the site. This means that the plugin completely relies on the template loading the BS files.

BS2 or BS3 ?
The BRB Plugin can either work in normal mode for BS3 HTML markup, or in compatibility mode for BS2 markup.
You can switch modes in the plugin configuration - go to Extensions->Plugins and filter for editor-xtd types.
Click the BRB plugin to configure it.
Select either the normal mode (NO) or the compatibility mode (YES)

In BS2 mode, all classes will be used for BS2 markup, e.g. span6, span4, etc.
In BS3 mode, the respective BS3 classes will be used for the HTML markup, such as col-sm-4, col-sm-6, etc

BS2 and BS3
What you should avoid is to load BS2 and BS3 at the same time in your website.
Loading both frameworks will lead to unwanted results, not only with the BRB Plugin but also generally, since some of the classes are defined in BS2 and BS3, such as the class .row or .container-fluid, they will influence each other.

This is NOT an issue with the BRB Plugin. If you load BS2 and BS3 in your site, unwanted behaviour may occur.

We recommend using BS3, since BS2 is already EOL.
Luckily, BS3 will be compatible with the upcoming BS4, so the BRB Plugin will also be compatible with this new version of BS.