I have used both WordPress.com and Blogger to host my blogs so I thought I would do a comparison. First let me explain there is a confusing difference between Wordpress.com and WordPress.org. Wordpress.org provides the free program that you use to write your blog on. However, they do not host your blog for free there. For this article when I refer to WordPress, I will be refering to WordPress.com.
Both WordPress and Blogger will host your blog for free. I cannot state this as a fact, but it seems on WordPress, new blogs get listed better on the search engines. They both provide easy to use, nice looking templates that will get your blog up and running in literally minutes. All of the templates on Blogger are free, whereas many of the templates on WordPress are free, but there are also some that are premium templates. Another difference is that on Blogger you can choose from many different fonts for free, however WordPress will charge you to "upgrade" to your choice of fonts.
I like both interfaces equally well. I think they both do their job, and any preference of one or the other would simply be a matter of taste. I know many people use and recommend WordPress if you are going to have your own domain hosted by a third party. I think both services look equally good and are equally easy for me to create content. However, I do like the way Blogger has the built in ability to "join" or "follow" other Blogger blogs. This is very popular on Blogger. WordPress offers something like it through a third party, but it doesn't seem as popular.
To me, the most difference is important difference is immediately apparent if you want to monetize your blog content. On WordPress, the Terms of Service prohibit advertising on blogs they host. On Blogger you can run ads from Google AdSense as Google also owns Blogger. You can also run ads from third parties like adBrite. In addition, WordPress has the right to put ads on your blog.
Ever since Google took away my Adsense account for no reason, I am not a fan of Google. I use Blip instead of YouTube (Google owned), however, I do use Blogger just because I want to monetize my content. I wish WordPress would allow advertising. What do you think? Who do you use and why?