A motherboard have a northbridge and a sothbridge.
The northbridge is an integrated circuit that is responsible for the communications between the CPU interface, AGP, PCI,PCI-E and the memory. The northbridge gets its name for commonly being North of the PCI bus.
The Southbridge, also known as the I/O Controller Hub (ICH), is a chip that implements the "slower" capabilities of the motherboard in a northbridge/southbridge chipset computer architecture. The southbridge can usually be distinguished from the northbridge by not being directly connected to the CPU. Rather, the northbridge ties the southbridge to the CPU.
The choose of the chipset of the motherboards depends of what processor you want firm AMD,INTEL-Pentium,or from Via , sockets(numbers of pins), numbers of processor (dual,quatro - on single socket or with many sockets - servers in general).
So you have to answer to other question before to know what is the best chipset for you.