What is your core competency? A self-hosted wordpress does take time to maintain, security updates and what not.

If I were to host a company blog (With no particular privacy concerns) I would probably use something like WPEngine.com. The cost per month is relatively small and if your company saves just an hour or two per month on maintenance, it is probably worth it.

Tumblr/wp.com is of course an alternative but it depends if you feel that they provide enough customizability for your needs.

Wordpress.com, for example, does not allow Google Analytics last I checked, and that was a big no no for me.

Edit: You can use Jekyll, octopress and so forth like others have suggested. BUT who are going to be writing/using the blog? Less technical users may not find those easy to use. The upside of both WP and tumblr is that they are easy to use for the average user.

I'd go with self hosted wordpess(or any other self hosted blog).

I don't really see it being professional hosting it on tumblr.

A more valid comparison would be Tumblr vs hosted WordPress (on wp.com). In which case, it boils down to personal preferences, assuming in both case you would do it at least a bit professionally (custom domain name + sort of custom theme, and not just mycorp.tumblr.com or mycorp.wordpress.com with a stock template)

Tumblr's a bit restrictive, but it's a simple option if you just want to publish quick posts of simple text and pictures. Blogger's a bit more powerful and you can do whatever you want on your own Wordpress. You'll miss out on some network effects though.

I recently set up pelican[1] for the engineering blog at $WORK. I really loved it's simplicity (I'm very comfortable with python eco-system).

[1] http://docs.getpelican.com

I went self-hosted Jekyll blog. Octopress is pretty nice too and I will migrate to it soon.

Wordpress requieres maintenance and you probably will use few things if you go corporate blog.