Depending on what you have access to I would recommend hyper-v. I used to use VMware but due to issues like expensive support and limitations with API on free version I decided to go with Hyper-V. As a Microsoft partner I get unlimited free critical support from Microsoft.
There is also a free version if Altaro which you install ib the host And will give you up to 2 vm backups for free.
Also if you want with hyper-v 2012 you get free replication which is really nice!!!