[Mashiro]

I would recommend KVM (opensource and free) or VMWare (if you have the money). Both are absolutely stable solutions and have great performance. KVM is huge in the VPS business and generally if you need proper hardware virtualization but it is also very advanced and needs a lot of knowledge to operate it on a higher level than the basics. VMWare is mostly a enterprise solution (atleast the product lines I mentioned above) that is used world wide by many multi million dollar companies and etc. It has many options and features, too. Also proper and advanced hardware virtualization. For private use VMWare has free products but they're rather short on features as they pretty much just have the basics.

If you're a huge fan of Windows you can use the onboard Hyper-V solution. We do that at work and it is kinda ok but I don't really like it that much to be honest.