it is the same for me. the only that you must look the pagerank of the site that you gonna submit the links
if you create free blogs, add post with your link, and never update it... i think it wont do much.. but if you're planning to update your blog regularly.. it could be a good source for backlink.. the good thing about article directories is that they are updated everytime and some already have good PR (at least google already give credit to them)
Article sites are good, so are blogs, but you have to keep it looking natural, I have seen way to many newbies try to build a thousand links in a week. Google knows this is an attempt to fool them and make your site look more important than it is to be bluntly honest. I would suggest finding article sites if you can in your niche, post to blogs directly related to your niche, and make sure you do it slowly, patience is key
best thing to do is combination of both, so the Google-bot thinks its all natural and submitted by different people.
if you have the time i'd choose both of them, as they say the more the better . Anyway if you intend to keep those blog and make some seo to them too they will become more valuable than article directories.