I have not been as impressed with hosting running NGINX as most people seem to be.
The problem is that the real bottleneck is the PHP when you get a server with multiple sites.
So at that point, it's time to look for faster PHP, not get stuck in Apache vs. NGINX - HHVM or I've been hearing great things about PHP 7.
You can also look at using Apache with Varnish to improve your speed and load times. I have reconfigured several VPSs with it and it works very well.
With NGINX ... I think you see the problems of using software with a smaller community. For example, there is less documentation, fewer available modules, less discussion, more being "on your own" with troubleshooting, and so on.