Here are the stacks I tested, on a DigitalOcean Ubuntu 14.04 LTS 1 cpu / 1gb RAM / 30 SSD / VM
1. LEMH (Linux. Nginx. MariaDB. HHVM)
2. LEPH (Linux. Nginx. Percona. HHVM)
3. LEMP (Linux. Nginx. MariaDB. PHP 7.0 )
Of the three tested, LEMP won this test. Not only did it use 752MB of less memory consumption it also has great performance. Not only that, LEMH & LEPH consumed 632+MB of memory on average. On a clean XenForo install!! that's crazy!
LEMP usage on a clean install. Haven't tested it yet on a live site. So I am not 100% sure how it handles clients.