I've worked with LOTS of virtualization hypervisors, and ultimately I would agree with hayabusa. It's a matter of preference.
VMware has been in the industry the longest so VMware Workstation or VMware Server have typically been the preferred choice. VirtualBox is open source, so if you like playing around with code you can do that. Even Microsoft VirtualPC is easy to use if you're in a Windows environment.
It used to be that VMware was the only vendor with USB passthrough, but now the other vendors have that technology too (though I have honestly had problems with USB in VirtualBox, but those problems were from a few versions ago and may have been addressed). I'd say it comes down to the reliability and capabilities in the VM tools that get installed on the VMs. In my opinion, VMware still has the upper hand in this area. But, again, it's a matter of preference.
"Live as though you would die tomorrow, learn as though you would live forever."
CCNA, MCSA, MCTS, Sec+, Net+, Linux+, CEH