At the moment, the reference version is Acceleo 2.6 and all the wizards and the menus of this version are available in an "Acceleo" category. We often use a "Model To Text" category for the next-gen version because we try to use the eclipse projects conventions.
There was a conflict for the Acceleo Perspective, because we can't give the name "Model To Text" to our perspective ;-) , so we decided to change the icon of the Acceleo 2.6 perspective by adding a small "2.6" decorator.
Finally, if you want to disable temporarly the next-gen Acceleo, you can disable the eclipse acceleo capabilities in the general preferences, as in the following screenshot.