You just really need to know what you need.
If you need USB, you should know that the first batch of MPX boards don't have working USB. So, AMD paid mobo makers to add a USB2 PCI card.
However, most of the MPX boards only have 3 *normal* PCI slots. If one goes to USB2, another to sound, and a third goes to the NIC, where will that FIreWire or TV tuner card go?
All MPX boards have two 64-bit, 66MHz PCI slots. Unless you have high-end SCSI or gigabit Ethernet, chances are you won't use these. And your normal PCI cards probably won't work in them either.
So, you really have to know what you want. Tyan gives you a 4th *normal* PCI slot and an option onboard Ethernet port ... but there will be no real overclocking. And tyan gives you an add-on USB 1.1 card, instead of USB 2.0. The Epox has onboard LAN too and should O/C nicely, but only three PCI slots ... with one likely going to USB2. Gigabyte gives you LAN and IDE RAID. Asus gives you sound. You just have to know what you want.
-SUO