When choosing between Apache and Nginx (or others), it's not really an apples-to-apples comparison, so you better look at the feature-set carefully before you choose to move. Apache has tons of features and has a great ecosystem around it, which means it can do a lot more to help you generate the content you need - e.g. server-side processing. Nginx is more geared towards high-performance, yet simpler content serving needs. Identify your needs, and then choose.
In a nutshell, if you are using mod_php, mod_perl or any of the esoteric modules with Apache in your current installation, I think staying with httpd is a better idea. If you are facing performance problems, you could use Nginx as a reverse-proxy.