I've never had any luck with blogs and social bookmarking sites, so for me it's posting in a popular forum.
If you have lots of friends on facebook, you can import your blog rss so it comes up as facebook 'notes'. Make sure to pop your blog or affiliate link in the post. Constantly amazes who reads your notes on there.
Are we to assume that all 3 receive the same amount and type of traffic? And, what type of website are you leading these visitors to? Do you sell a product or is it just informational?
Lets assume they are for the same niche and the only thing being promoted is the article. Where do I post the article?
I will say first in a popular forum than Squidoo lenses also . They also get good traffic in rotation .
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popular forum or a blogspot blog that has been optimized for a related keyword to your niche, while ensuring the click-thru rate from the blog is good. But there are less barriers to entry in forums