collaborative documents

Today a few of my colleagues and I are testing software to work on collaboratively.
We selected three possibilities a pbwiki, coventi pages and google documents. All of them have different applications, so we will have to see which software we like the most.

For what: to get six syllabi that cover the same topic - but are given by different professors - to get them all into one final syllabus that covers the content and is satisfactory to all. That is why we are looking for something that keeps track of all the versions and allows easy comparison between versions.
The software also needed to be as intuitive as possible because of the difference in computer literacy.