Joomla is great for beginners, and has tons of extensions. Drupal is versatile. Wordpress has some VERY nice templates. I've recently discovered Magento which is great because it is innately geared toward an e-commerce site.
I recommend Drupal. The community is fantastic, and I find it easier to learn than Joomla. Drupal has a more "page literal" backend, where there are extra functions on the page that you have abilities to customize. Joomla however, has a (in my opinion) more abstract backend, with a whole new interface aside from what the site looks like that might take a little longer to learn. At least for me it did.
I also prefer Joomla, because I know it better, but there is a CMS less known, made in Denmark (but it's available in English) and it is also very nice. The name is Umbraco. Of course this is also free.
I think it's worth to give it a try.