Personally, I think you should have it on your own domain as a part of the main site.

Here's why:
* It immediately adds more relevant content pages to your site
* You can submit your blog to Blog Directories (which I will list below). Giving you more traffic and backlinks (that even helps your main site)
* You can leverage the blogger community to drive traffic to your site.
* You can keep your content current.
* You can broadcast changes to your site via Ping.
* Your site can be found in Blog specific search engines.

See the original post here: http://www.greatnexus.com/blog/16.html