Wordpress.com is nice and clean and free and very user-friendly. Plus, once you get more advanced, it's an easier transition to Wordpress.org. The only downside of Wordpress.com is that its restrictive in terms of widgets, advertising and custom themes.
Blogger.com is very, very easy. Lots of themes, lots of widgets and you can integrate analytics and advertising right out of the box with a single click. Very social-able, too--easy to have people follow you and follow others. Plus, it's Google, so it's good.
I haven't really used any other platform extensively. Typepad is notable, but never tried it.