What is a good way to have a Linux server with a robust virtual environment?

I'd like to have Linux-based server with a robust virtual platform, same as ESXI is for Windows. The hardware is a HP Server with 16GB of RAM, 1TB of hard drive and Intel XEON 3.7GHz.

The hosts are going to be sending/receiving Internet traffic and running some security applications (firewalls, IPS-intruder prevention systems...). The traffic will be also analyzed by a commercial tool similar to Wireshark.
Based on what I understood, I may consider these options:

1. Ubuntu Server + KVM + vSwitch
   
2. CentOS + KVM + vSwitch
   
3. CentOS + Xen + vSwitch
   
4. openSUse + KVM + vSwitch
   
5. Debian + KVM + vSwitch
   
6. oVirt?

What would be the best option for the applications I want to run?