Asterisk PBX installation & setup on OpenVZ virtual machine

Moving our office PBX to a voip based system that we would like to run on our Proxmox PVE 1.9 virtualization servers. We want and experienced voip system administrator to advice on the right distribution to use... currently considering Asterisknow, freepbx or elastix and then install the basic system under a virtualized OpenVZ environment. This means that the setup will have to be done from scratch on either CentOS, Debian, etc based OpenVZ appliance. We want the system to be as clean as possible and exclusively include packages for the PBX services. Ideally this installed from repositories so future upgrades can be simple enough. No PBX hardware to be installed initially so this should not be an issue to virtualize. The system should include 2/3 basic trunk setup, a few groups and some extensions, and basic setup so we can handle de rest of extensions / routes ourselves. We will supply a detailed initial list... each user to have 2-3 extensions for softphone, ip phone, etc Job will be delivered as tgz snapshot OpenVZ virtual machine based on PVE 1.9 with bridged network configuration (details provided) that we can restore and run directly on our system. The candidates should post apart from rate... recommended platform to use (for PBX) and OS with version (CentOS, Debian, etc)