I agree with Christina that Twitter does a better job exposing your blog.
Here's a few things to think about:
Facebook has an algorithm that determines if your posts show up on a news feed (unless the person changes their news feed to most recent). It is based upon the interaction with your posts, so the more likes and comments on a post, the more people will see your post. Does that make sense?
With Twitter it is all in "real time" so the issue with Twitter is, if someone is following, say 2,000 people, your post is only on their news feed for a short time. If they are not on when you post, you may not reach them.
There are a couple of tricks to this,
#1. When posting on Facebook, aim for quality posts that will attract readers and encourage them to like and comment on your post. A good way to do this is to post a question, or post something from other sites that are popular as well. The interactions on you other posts can slightly boost posts that are not getting much interaction.
#2. When posting on Twitter, still aim for quality, but you want to aim for quantity too. Post several times throughout the day, not 15 posts in 1 hour, but 10-15 posts throughout the day. You also want to post during the times that you get the most response.
I hope this helps!