What is the difference between different virtual HD formats?

I'm creating a few virtual machines to play with, with a few different OSs to test, using VirtualBox.

The question I'm against is about the HD images files that it uses. When creating the virtual media, it ask about which format to use, I'm given the following options:

• VDI (VirtualBox Disk Image)
• VMDK (Virtual Machine Disk)
• VHD (Virtual Hard Disk)
• HDD (Parallels Hard Disk)
• QED (QEMU enchanced disk)
• QCOW (QEMU Copy-On-Write)

Which one should I choose? Or which criteria can I use to select the best for each case?
Any advantages/disadvantages to each one?

At first, I started using VDI, the VirtualBox native one, just because it was the default (what a good criteria (?)). The, switched to VHD, the VirtualPC native, just for the sake of Windows being able to mount it outside the VM, natively (all others requiring external tools), which seemed a nice feature to me.
Any suggestion? Thanks!

whs said:

VDI is the vBox format. VMDK is VMware and VHD is Windows. The others I'm not sure.

Thanks, already saw that. That's just who created each HD image type, but tells nothing about how to select each one.

My question was more geared towards knowing the pros/cons of each one, since at least VirtualBox can use them all.