WordPress.com is perhaps the most feature-rich blogging service out there. It uses the popular open source web software WordPress, and offers many features in its free version — traffic stats, anti-spam filters, SEO, gorgeous themes and more.
Blog.com is another popular WordPress-powered blogging platform.
Just like other services, it has its own share of pros and cons. For a start, it offers many beautiful premium themes in its free accounts, as well as advanced plugins that one can expect only on a self-hosted blog. However, on the downside, the free service displays more ads as compared to WordPress.com. (But you can opt for paid upgrades to remove the advertisements.)
The free storage space offered on Blog.com is 2GB in the basic plan, which is less compared to 3GB that WordPress.com gives its users.