Change visudo editor
By default, Ubuntu uses nano for editing visudo.
Nano is the linux editor for Windows administrator . . . don't use it!
To change it to something else, such as vim:
sudo update-alternatives --config editor
There are 4 choices for the alternative editor (providing /usr/bin/editor).
Selection Path Priority Status
------------------------------------------------------------
* 0 /bin/nano 40 auto mode
1 /bin/ed -100 manual mode
2 /bin/nano 40 manual mode
3 /usr/bin/vim.basic 30 manual mode
4 /usr/bin/vim.tiny 10 manual mode
Press enter to keep the current choice[*], or type selection number: 3
References
vim - the docs http://vimdoc.sourceforge.net/