"the best of x && y" is a question that we face on a daily basis in the IT world. unfortunately it's not all black and white. every tool excels at one thing and not the other. so it all comes down to your needs.
for example, if you're going opensource, i suggest you checkout proxmox . it has an amazing interface that can help you configure every option of both openvz as well as kvm. on the other hand, if you have the budget, i suggest to go with vmware vcenter . coupled with ESXI you'll be set to go. PS: if there are budget constraints and your farm of servers isn't big to begin with. you can use ESXI with vcenter trial. configure it all together and then just get rid of the vcenter once the trial period is done. though there's a lot of features that you'll be losing by doing so. since after all you get what you pay for :)
