In the early days of my server-career, I had to use lighttpd for RAM-reasons. Over time the limitations of lighttpd were mounting. E.g. no .htaccess-files, no auth with certificates, bad DAViCal integration, inconsistent LDAP-filters. Moreover after some time lighttpd uses up more and more memory.
So for now I'm just using both of them to compare performance and overall ease-of-user.