In my experience, if you need to implement a site based on a psd from a designer, go drupal, if you suspect the site you're building will end up having lots of extra stuff bolted on in the future, go drupal (this almost always happens).

The only case I would go with wordpress is when someone wants a blog with a few extra pages and likes an existing wordpress theme, that's it.

Because the moment you have to make something pixel perfect, or you have to turn a site which started off as a blog into something more complicated wordpress will make your life miserable compared to drupal.

Basically, just go drupal.