Apache is pretty much the standard for a lot of companies so you can't go wrong with learning that. But you should def. do some reading on nginx, and lighttpd as well
For example, Apache has a lot more modules that can do obscure things that aren't mainstream for a web server. Such as LDAP, and WebDAV, these modules might make Apache better suited for an intranet setup. Even if the nginx community popped out a good WebDAV module, the Apache one would still be a better choice because of the vast documentation and larger user base and community support already available for it.