The nForce 2 supposedly has wonderful performance. It will be good regardless of what you equip it with. However, if you equip it with a very outdated video card, like a Voodoo 2 on a PCI slot, you are going to be limited by the quality of that particular part, no matter which motherboard you stick it on.
The nForce 2, however, does suffer from some compatibility/stability issues, and is made by Nvidia, a company displaying microsoft like characteristics (it seems to like they are trying to take over the whole computer market - what I mean, how long before we see Nvidia sound cards or CD burners, for those of you following my conversation). I personally will not choose to support Nvidia in this respect, and they are new to the motherboard arena (they are primarily a video card maker), and SiS is more stable and compatible.
The SiS 745 (currently the best Socket A board SiS offers) can't compete performance wise with the nForce 2, but the upcoming 746FX should wipe out the nForce 2 (I don't know when SiS will release the 746FX).
I personally recommend MSI. On my particular board they made some hardware changes like adding an additional heatsink, they are one of the only vendors who made a model with integrated Firewire (the 745 Ultra-E), and they have their signature red color for their circuit boards (kind of like how Gigabyte uses blue).
I was also very impressed by their software/drivers CD. They had automatic BIOS updates and everything. I would recommend MSI is a vendor also as they aren't priced higher than Asus. MSI stands for MicroStar Incoporated.
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Benchmarks don't lie 🙂