I've used WP, but haven't used drupal or joomla.I guess those three would be the most popular3 that are most alike. I've also used another one called Mura, but its Coldfusion based.
I've heard drupal and joomla have a bit more learning curve. Either way, as far as easy projects for clients, CMS's are the way to go IMO. Once you set up your first, they get easier, and make for quick completion which means quicker paydays..lol