I have been using Posterous for Smileecards blog (http://blog.smileecards.com/), but recently have started using Tumblr (http://smileecards.tumblr.com/) as well to try to put content in different places.
I'm mostly using the basic features of these services and I like both services so far, but have found Tumblr to be easier to use; it's more intuitive to me.
I dislike the interaction of the image manager in Posterous, especially if trying to add multiple images to a post. I also don't like the difference in white space between edit and view mode of posts.
To the audience - what service do you use for your blog and why? Posterous, Tumblr, Blogger, etc.