There are a lot of considerations to make when using virtualization technologies. Finding a solution which balances performance and security can be challenging. Likewise, use case is a significant factor—a desktop-focused hypervisor would not be a good fit for creating virtual servers.
SEE: Comparison chart: Virtualization platforms (Tech Pro Research)
For server use, the most optimal solution may come as part of your OS. In Linux, the Kernel Virtual Machine (KVM) and Hyper-V in Windows are included by default and require no additional plug-ins to run. Being integrated into the OS removes a layer of frustration in configuration.
Alternatively, partial virtualization solutions use less overhead. OpenVZ allows for multiple instances of Linux to run on the same server, but with the added limitation that all installed guests must use the same base kernel. Software containers such as Docker have also become increasingly popular, as apps can be run isolated from the host environment without the overhead of running a full virtualized OS for each guest.
Server virtualization can also run headless. Solutions such as XenServer, VMware Server ESX Server, and Microsoft Hyper-V server allow for virtual machines to be run and managed from the virtualization server platform without needing to configure and manage a full host OS from which virtual machines run.
For situations that call for running programs from a different OS—for example, a Linux user needing to run Windows software that lacks a native equivalent, like GRLevel3—a virtualization platform intended for desktop use would be more convenient.
The open source program VirtualBox is often the first choice for such situations. VirtualBox is user friendly for people unfamiliar with virtualization. It supports Windows, OS X, Linux, FreeBSD, and Solaris hosts and has extensive guest support for both mainstream and boutique or niche operating systems, including OS/2 and Haiku. It also has a seamless mode, allowing guest app windows to be run directly on top of the host OS.
VMware Workstation (as well as the free VMware Player and the OS X equivalent, VMware Fusion) is the most popular commercial option. VMware has more extensive support for UEFI emulation, as well as support for disk snapshots, and much more robust support for 3D graphics acceleration than VirtualBox.
SEE: VirtualBox: Everything the pros need to know (TechRepublic)
Do you need to virtualize?
Depending on your use case, using a compatibility layer such as WINE can be a more efficient way of running Windows applications on your non-Windows computer. Instead of virtualizing an entire computer, WINE is a free re-implementation of Windows components that can be ported to other systems. While WINE is free software, the commercial Crossover program offers more configuration utilities, along with a Chrome OS option for running Windows programs on Chromebooks.