Radio Free Blogistan has a recent entry comparing Blogger to Radio Userland.

Among the differences:

• The Radio client runs on your desktop computer; the Blogger client is browser-based.

• Radio Userland has a lot of built-in 'ping' functionality (ability to send auto-notices to sites that track new blog updates.

• Blogger provides a 'blog this' shortcut that makes it easy to do a blog entry for the web page you're currently on. Radio doesn't seem to have a similar feature

• Radio Userland makes it very easy to subscribe to syndicated news feeds and to blog entries received this way.

• Blogger is free (though there is also a pay version: Blogger Pro); Radio Userland is $40 per year with a 30 day trial period.