blogs or message boards?

If the goal is to get students writing thoughtful responses to course materials and questions and for them to regularly read and comment on other students' posts so that they are engaging each other, is the best tool blogs or message boards?

Blogs might encourage longer posts--not that longer=better but a message board might seem like a place for a quick thought rather than a more developed response. But blogs stand separately, so the discussion might stay on one student's blog and not cross over as much as it would on a message board, where the various threads are all in one place for students to see all at once and click through easily.

It also seems overwhelming to require all students in a class to read all of their classmates' blogs, probably reducing the number of comments each blog would get. This semester, my students are only required to read the blogs of their group members, and the blogs are tied directly to a collaborative project. A message board might facilitate easier exchange among a larger number of class members.

Several years ago as a student I was in a large section of a course (maybe 75 students) with a message board, and it was fairly easy to keep up with the discussion, even with that many course members. But I'm sure that many students sort of fell by the wayside. It also meant that fewer people actually initiated discussions, but more people responded to the posts of other students. Depending on the goal of the exercise, it might be okay if only a handful of students are the initiators as long as the rest are thoughtfully discussing the ideas.

I am considering this question broadly for use with various kinds of classes but also with an online section of Advanced Composition in mind.

Hmmm.