Some intelligent people managed to screwed 'visudo' using nano 8-O to edit the sudoers file... why not create a nanosudo command?...
Anyway to have a REAL editor:
<code bash> 
export EDITOR=`which vim`
visudo
</code>
tip add the export line in the ~/.bashrc of root ;-) and your user's .bashrc/.zshrc as all is for dummies now with nano...