Ars put Parallels 8 against VMware Fusion this week and found there is not much of a contest between the two virtualization powerhouses. Parallels 8 out-gunned VMware across the board (as previous benchmarks have shown) performance-wise and adds full support for Retina displays and dictation among other features.
Neither Parallels Desktop 8 or VMWare Fusion 5 are loaded to the gills with new features, so the PD8 update from version 7 is only a must-have if you are looking for Windows 8 or retina MacBook support in Windows 7 or 8. If you need retina support, this is your best option since Parallels did the extra work and made it a better retina experience than in VMWare Fusion 5. The Mountain Lion dictation and experimental DirectX 10 support show that, while Parallels tends to have more frequent paid updates and a higher price-tag, they try to earn the extra value with well thought out features and engineering. Apart from the bugs I saw in Mountain Lion 8, I think Parallels Desktop 8 earns that extra cost with its solid performance, far superior Linux OpenGL support, and existing feature set. But if your needs are more big-business-oriented, VMWare Fusion 5 Pro might be more your thing.
VMware Fusion might fit better into cross-platform installations or for folks with legacy VMware images.