VMWare Player [for personal use] VMWare Workstation [what we use in my current company] Microsoft Virtual PC [if you don't care about USB] VMWare eSXi [if doing bare metal virtualization] just really depends on needs and usage ^_^
I think it really depends on your needs. I personally use VMWare Workstation. If you need a free virtualization software VirtualBox is a great alternative.
Wow let me see the vote results. It seems everybody liked VMWare Workstation more. For my current status: I originally would vote for VirtualBox (since I'm using Ubuntu now and VMWare just can't patch the kernel) however VirtualBox simply can't boot USB sticks, and since I'm now building Chromium OS builds that doesn't help. So my vote for now: Abstain.
Symantec Workspace Virtualization (SWV) is my favorite. It was formerly known as Altiris SVS. Intended for business use, but is free (unlimited trial) for individuals. Application level virtualization. For me, it puts the fun back into computing. Help to keep the OS clean.
I like Hyper-V and VMWare Workstation, but they can't run side by side. I chose to keep VMWare for the 3D performance.
I use Oracle VirtualBox often. I like it a lot. It is easy to use, and works fine with the Windows I install. I use sometimes Windows Virtual PC, but it does not support Windows 8, so I will probably end using it completely.
I couldn't install Windows 8 Pro in VirtualBox so I switched to VMware Workstation 9 and I installed W8 very easy. I say VMware Workstation.
I installed Windows Hyper-V core 2012 (baremetal) on my new machine: I7-3770S, P8Q77-M2, 32 GB mem, 240 GB SSD, 1 TB HDD (hardware configuration fully supports all Intel VT technology). It's lightning fast and its free (Windows Hyper-V core 2012) (you can also run/boot hyper-v core from a USB)
Backup options (not tested): 1) Schedule a windows backup within a VM to an external share/nas. 2) Copy a not running VM to an external drive within hyper-v core 2) Replicate the VM to another server (on a other location) 3) Create a Virtual Harddisk on a network share where the drive is located on a other system/location/nas (share has to be attached within hyper-v core). Schedule a windows Backup within a VM to backup to the virtual backup disk. 4) ? Don't use SnapShot's as a backup. It's fine for a lab scenario but not for backups. Snapshots and Exchange 2013 RTM is not supported. Always make a snapshot of the DC and Exchange server (both not running) otherwise you won't be able to travel back in time.
Being a noob, I can't vote. I began playing with VMware Workstation 9.02 about two weeks ago. Wow, I could just kick myself. Prior to VMware, once I had a "playing around OS" ready for evil experimentation, I would make and verify a backup image, which took at least 45 minutes, plugging/unplugging and reboots. What a P.I.T.A. VMware is just great for me. I wish I had paid attention to virtualization years (and countless hours) ago. (Why doesn't somebody TELL me these things?)