If you are using Super Socializer plugin to enable Social Comments, follow the steps mentioned below to disable default comment form from Social Comments.
Change the Order of tabs in commenting interface in Social Commenting section at Super Socializer > Social Commenting page to facebook,wordpress,disqus (keep WordPress at second place, arrange others according to your needs) and save changes.
Add following CSS in Custom CSS option at Super Socializer > General Options page in admin panel
li#theChampTabs-1-li{display:none;}