We determined several differences in performance between the tested chipsets, but we could not make out a clear overall winner or loser. In practice the differences aren't very big, so that a really well tuned board with chipset A can beat a less optimized board with chipset B.
In this case, a recommendation based on better performance would be questionable. We do see the following differentiation: If the product price is especially important, the chipsets from SiS and VIA come out on par; the choice can go to either one for most users.
As far as overclocking is concerned, there is no winner in this contest, either. VIA has offered a fixed AGP and PCI rate since the K8T800 Pro supports HyperTransport and thus allow the Athlon64 to move towards maximum speed "without danger" - but this feature is hardly used by the boards available on the market due to their unreliability. Boards with the 755FX from SiS tend to be aimed at the lower-end market segment, so they do not generally offer useful overclocking functions.
The nForce3 Ultra is way up at the top, price- and functionality-wise. It is the only contender that offers an integrated gigabit network controller, including an innovative firewall, as well as four SATA ports. Unlike the new Intel 915 and 925 chipsets, the manufacturer was content with two UltraATA/133 channels, thus ensuring support for older hard disks and optical drives.
When the next chipset versions come out later in the year, it will be time to reshuffle the deck, especially with each manufacturer following a different strategy. The new boards won't be any faster, since all the performance relevant factors are part of the processor with the Athlon64. If you can live without PCI Express, you are sure to find a good deal when autumn arrives.