Recently, a coworker asked me an SEO question, “If I have a blog, is it better to have it on my site or do I get more credit for having an external blog link to my site?” This is an excellent question.
From an SEO perspective, I think it is better to have the blog on your own site for the following reasons. When you create good content, people will link to it (a blog, if written well with keywords in mind, is good content). If you host your blog on an external site, you will only have 1 link to your site (from the external blog site to your page) and other sites will link to the site where your content lives (giving the external blog site credit for those links in the engines). When considering organic engine rankings, multiple links to the content on your site will always benefit you more than having only one link from an external blog site.
Its simple, when building a website with SEO in mind, it is important to build community and content. The more topics you can add to your blog, which are relevant to your site, the more reach you have. When people see the content is relevant to their site as well, they will link to it, and when they link to it, you are more likely to reach your target audience. This is all contingent on relevant copy of course.