Different from most blog search engines, Google blog search ranks its results by relevance. You can customize it by clicking on "sort by date", but the default is useful if you want to find the most substantial blog posts.
But how does Google rank blog posts???
Links from quality sites
The number of feed readers
Clicks in search results
Links from mail, chats etc.
Posts added at a certain time
The size of repeat content
Using words that appear frequently in spam Blogs
Linking to a one web page
A large number of ads
We cleared that Google uses all kinds of factors to decide the popularity and the quality of a blog. But this doesn't mean less popular Blogs are dropped out if they have relevant content. But you should try to avoid the cons that may signal that the blog is spam.