I'd have to cast my vote for Joomla! on the basis that it offers a tremendous amount of flexibility, has a massive user community and a seemingly endless supply of extensions.
Don't get me wrong. Both are quality choices. Wordpress is a bit easier to use out of the gate, but in my experience Joomla! is simply more customizable/flexible.
Search engines love Joomla!, though you can't go wrong on that count with Wordpress either.
In the end, it may come down to finding an template that just "fits" for your concept.