Have picked up playing again and wondering if there is a addon that works like http://war.curse.com/downloads/war-addons/details/nerfed-buttons.aspx for WoW.

No, because Blizzard doesn't have events or APIs for spell prioritization in the way you are thinking. However, an addon can suggest in a roundabout way what is best. Check out http://www.wowinterface.com/downloads/info11935-EventHorizon.html

Thanks, will check it out