Is it better to have a blog on my site or to guest blog and submit articles to other sites?

[Jake]

A blog on the same url will generate more link juice than linking a separate blog to your main site.

Those article directories which took a hit from the Panda filter are not as powerful, a site for redistributing articles with author links like ezinearticles,com might be better for solid material people would want to reprint.
Some say negotiating to write guest articles for influential sites with better ranking than your own may be the best use of your effort, along with content for your own site.