This site has a blog comparison chart.
The three platforms I looked at are Blogger, WordPress, and Edublogs. I don’t think a person would go wrong with any of these. None of them require technical knowledge. They all have the ability to support multiple authors, can be made private, and be ad-free. Student accounts can’t be managed through WordPress, but they can be with the other two. WordPress is also the only one that can’t support embedded media from a third party. Edublog doesn’t require users to be 13 or over as the other two do. The only other difference mentioned in this article is that Edublog offers few themes than the other two. None of these differences seem very important, so it appears that users could be satisfied with whichever platform they picked.