Natural Search Software

What do you recommend: one blogger for a company blog for a unified message, or multiple authors from different departments for multiple viewpoints?

Of course you have to preface this question with stating your blogging goals. From a goals standpoint, you know I'm always going to focus on two areas:

Blogging as a tools for SEO
Engagement by the reader

So in light of those goals I would argue that it is better to have multiple authors. The best blog content for businesses, centers on stories about the product and customers who use the product (or service). Think about it, people come to your blog to help them solve a specific problem: The problem they described in their keyword phrase. By telling stories about that phrase and how you have helped people in similar situations, you gain high engagement from the reader which transforms into conversions.

The people best at telling these kind of stories are probably not your CEO, more likely they are the folks who work in customer service, sales people, product managers or developers. Whoever is closer to the customers. A big part of SEO is based on frequency. This is another area that makes business blogging better than traditional websites for SEO. The more frequently your blogs are updated, the better chance they have to be found. Saying that, it's better to have a lot of people participating....naturally you get more content.