If you mean contents only and need SEO based CMS, I prefer for wordpress. It's a blog platform but have many features to manage contents really. You can customize url as you wanted and can add different meta tags (keywords and description) for each post/page also. However, Joomla + SEF is also good but not all components can be supported by SEF components. Drupal is excellent one but need skills to make it work, not easy like Joomla for noob.
I've successfully used WordPress and Drupal but they do different things well... Drupal is used for its community features - forums, photo uploads, allowing user blogs and so forth, and those get well-indexed and provide a variety of user input options. For a community-centered site, Drupal fit the bill a lot better than WordPress or Joomla or any other CMS, and it's relatively easy for our members to figure out and use. We don't do anything fancy with it - it's got a standard theme installed and host of plugins, but it pretty much just offers an online gathering place for folks to use - www.simonskungfu.com - and the folks who own that site manage it themselves - it's not THAT difficult to use. But I use WordPress on two other sites that are more for conveying information. It's a bit different to manage than a Drupal system, but there's a TON of documentation from the open source community on how to use it and tweak it. One of my favorite projects is a WP site - www.thefixchicks.com - we have the occasional user contribution, which was why we went with a CMS instead of a simple content delivery method. WP developers are more SEO conscious too - there seem to be a lot of extra tweaks that are specifically designed to improve page relevance, for example... But I think you should pick your system based on the job it has to do - not how SEO-friendly it is.