Unlike Zen and Aurora, which stand on the lighter-weight side of Drupal base themes used for responsive theming, the Omega stands on the opposite site, as it is a feature-rich, Sass-based theme. The theme became very popular in its third installment, but version 4 is already out and most coders use it now.
Used for responsive design, Omega 4 has quite a lot to offer. For instance, it offers an innovative layout system that lets you define context-sensitive layouts, each with custom regions and CS, it hosts a complete rewrite (“cleanup”) of all of Drupal core’s CSS, a development extension with tools for things like LiveReload integration, a region demo mode, a browser width indicator for responsive theming and much more.
Packed with feature-rich tools, Omega has a powerful setup out of the box that can improve your productivity, but also feel bogged down by having to do everything a certain way.
Omega is a very popular theme, so there’s a big community behind it to support it. A lot of coders are working to find and fix issues and bugs, so you don’t have to. However, lots of programmers still use Omega 3 although Omega 4 is out.
Omega 4 is not yet the most popular of the Omega versions, but it will surely become in the near future click for more. At the same time, lots of the documentation and QA you find on Omega is actually for Omega 3. On the other hand, the official documentation for the 4.x version is well written and quite extensive.
Using the Omega theme for responsive design means that you will be setting up a subtheme of Omega which you will alter with the full power of Sass/Compass for best results.