To choose you default login personality click on your name in the top right corner and go to My Accounts < Personalities. The click on the personality you would like to be your default and "Select as Default Login Personality" under the Basic tab.

Additionally, each user can also choose which personalities appear inside their account menu and which are hidden. For example, if you are part of a large team with many personalities, you can now hide those you do not use.

To do this, click on your name in the top right corner and go to My Accounts < Personalities. Use the toggle switches to the right of the personality name to hide the personalities you do not need to appear in your dropdown menu.