Blogger is growing on me. The biggest things in its favor, versus WordPress.com, are the template editing and the profile features. I haven't played with it much, but I'd have to give the new templates a solid 10. Now that I can tweak the HTML and CSS, it's pushing an 11. The profile thing is just right, even though it hasn't changed, I don't think, in years. My only gripe is that to add a picture, you have to be running Windows. Of course that's a non-issue for 90 plus percent of the world.
WordPress.com is formidable to be sure. It has powerful tools for tracking your traffic built in. The thing I like best, however, is its comment tracking feature. With it, you can track your comments all across WordPress.com from you dashboard. It's really nice. It's more of a community over there and it's all sort of self contained. I don't like the stock templates, though, and you can't edit them unless you pony up a little cash. (I don't mind that, but I don't have any to pony up). Additionally you can add an avatar to your profile and it appears all over the WordPress.com when you comment, and even in a tag tracking feature that needs some work. Additionally WordPress has a "page" feature that permits permanent, static content to be linked to from the main page.
If I could only use one, today I'd probably have to go with WordPress. I've enjoyed their work for a while now. They're more of a hacker community. I like that.