For me the Google Blog Search was both the most confusing and the easiest to use. When I first started playing around on it, I was very broad on my search topics. After playing with it for a little bit, I realized how specific I needed to be. I was then able to manipulate it to bring up more of what I was looking for and not just fluff.
One of the best tools I found when I was looking at blogs came from http://janeknight.typepad.com/pick/. I love Wordle.net and so when I found http://www.tagxedo.com/ I fell in love. It is basically Wordle but it puts the word in to a picture for you, such as an apple, heart, etc. You can even upload the picture you want the words in the form of. I cannot wait to share this with my students and staff!!!