Sometimes I use Aptitude in visual mode to install and upgrade packages.
When I upgrade from the command line using
aptitude I often use
full-upgrade instead of
safe-upgrade because I run the testing flavour of Debian, but which one is used in Aptitude visual mode?
Basically, what really happens when I press U?
If it's one way or another, is there a way to configure the default behaviour, or to decide manually which one to use?
 The GUI. Some call this a TUI.
 Formerly called upgrade and dist-upgrade respectively.