I like both WordPress and Blogger - for slightly different reasons.
Both are free to use if you only intend to set up a basic account!
Why I use WordPress
There are plenty of things that make blogging on WordPress a pleasure.
I find that even the non-premium account still provides users with a host of cool features (such as traffic stats broken down by demographic or geolocation). It even has its own built-in spam filter!
WordPress also gets bonus points because so many "serious" blogs are published on the platform.
Everyone from CNN to Flickr communicate via WordPress blogs, adding an extra dimension of trustworthiness or credibility to the platform, which is something I think other blog platforms struggle with.
What's so great about Blogger?
There are two things that really attract me to Blogger - both of them are related to the fact that it is owned and operated by Google.
Firstly, you can go from setting up your blog through to publishing your first post in under 15 minutes. Typical Google streamlined user interface.
The second factor is that, as a Google product, it is really simple to link your Blogger page with a Google AdSense account - helping you earn some dollar for all the hours you put in to carefully crafted blog posts!