A Wiki or a Blog

I am still trying to decide what I should turn MomsOpNet site into. I am leaning towards a blog but I have also seen some really nice wikis. My goal is to make the site very easy to edit and to be able to add contributors to the site. I am actually not exactly sure of the difference between a wiki and a blog. I think maybe it's mostly the design and layout. I know how to create a free wiki because I have found a number of sites like this one. I am going to have to make a discussion soon because I need to start the changes.