Traditionally, only Vmware has had 3D support, of a sort. They still don't provide any pixel shader support, only provides some DirectX8 and because of the slow response, even at 1000Hz kernel timings, unusable for gaming. Conversely, Parallels is roughly $100 cheaper than Vmware, provides no 3D support and responds considerably faster than Vmware although not perfectly. Additionally, to my knowledge, only Parallels allows you to jerry rig together various USB devices such as printers and get them running with the VM.

In order to contrast them properly, I'll attempt to tackle each facet individually and give examples where necessary.

DirectX and OpenGL.

As I've mentioned before, only Vmware provides DirectX support, of a sort, at this point. This with the vmware tools drivers installed in Windows. lLnux can do svga without having to install vmware tools as xorg includes OSS vmware drivers although I've never had occasion to test the speed of the linux xorg vmware drivers. This is something that Parallels does not do. Currently Parallels does not have 3D acceleration, this is a problem for a company which has promised to have 3D support by January 2008. Also, unless they find a way to get the interrupt working faster, the jitteryness would still be too much to play any games properly.

Ease of Use

Both work about the same. It's true that Vmware has become somewhat “feature heavy”, or at least it's said that Vmware has become feature heavy. Personally I've never seen a feature I didn't like and the overlap between the two programs is almost total.

The two main differences are

1. Vmware enables you to take snapshots of virtual machines.

2. Parallels has better USB device support.

Sound and Networking

Identical. The main differnence is that Parallels configures the networking slightly faster than Vmware does. Otherwise both can play sound and both are capable of three types of network connections.

1. Host only

2. NAT from Host

3. Own address assigned to host's interface

Overall

They're both excellent products. Trying to play games on either is pointless if they invoke any remotely advanced 3D requirements or if they require fast twitch reflexes. For a desktop virtualisation solution, I would pick Parallels because of the price; although for running linux, Vmware might be a better choice if you can afford it.