How can I set the default user role as Administrator for new users?

How can I set the default user role as Administrator for new registrants?

I have the following plugins:

Multisite User Manager
User Role Editor

I have set the default role for all my sites as Administrator but this is still unclear weather new users will have that title as default.

Can someone clearify how I can be sure users are assigned the Administrator Role at Sign Up. (or any role by default for that matter.)