Joomla has a big developer community and lots of extensions so probably your best bet for the type of site you are proposing - the way it is put together is not the greatest, but unless you are a very experienced coder and get get to grips with the likes of
Plone CMS: Open Source Content Management its the best you'll get. EE I find clunky and my clients do too.
Wordpress is the best CMS I have found once you have configured it away from being a blog - the formatting tools are easy to use and produce good code, but its probably not suitable for the site your proposing.
Modx looks interesting - would be interested to hear from experienced developers using this re: some work possibilities?