The best Content Management System Plugin

Hello,

I am developing a site for a client and i want to allow them to edit the website themselves. I understand that WordPress IS a CMS however my client does not know anything about WordPress.

What is the best way for my client to do this? is there a plugin or will i have to disable certain elements of the WP Dashboard and teach them the basics?

I think my main issue is that for some pages i have set a modules width and height – thus if they were to lengthen the content it wont appear as it extends beyond the widget area.

Any help would be a lifesaver!

James