Here are a few reasons to consider the Gigabyte board:
1. My computer is based on the ALi Aladdin V chipset; my Fianceé used to have a computer based on the SiS 530 chipset. My computer slaughtered hers in memory benchmarks.
2. Check to see how much L2 cache is included on your motherboard. This will decide how much maximum RAM you will want to install on your system. The SiS 530 chipset can only cache half the amount of RAM that the ALi chipset can. If you have 512KB L2 cache on the motherboard, the ALi chipset will be able to cache 128MB RAM, while the SiS chipset will only be able to cache 64MB. With 1024K (1MB), the ALi chipset will be able to cache 256MB RAM, and the SiS, 128MB. Any RAM used above the cacheable limit will be accessed very slowly, and will have a noticeable performance impact, especially in games. The problem is that Windows loads itself into memory from the top down, so the performance hit is seen right away, not after you've already filled up the said limit of RAM. This is because Windows loads into the uncached area of RAM first.
If you have an AMD K6-III processor (and maybe the AMD K6-2+, I can't remember), you will have L2 cache on the chip itself, which doesn't have such a limitation (in this case, the L2 cache on the motherboard becomes a L3 cache).
3. The ALi Aladdin V chipset has no problems with the Sound Blaster Live! or certain network cards. This is because the PCI bus doesn't get interrupted like it does with VIA chipsets. I can't vouch for or against the old SiS chipsets, since I have never tried a Sound Blaster Live! with them.
4. This is the most stable motherboard I have ever owned (BCM VP-1541, very similar to the Gigabyte board).
Things to be aware of:
1. People have reported problems on many Super Socket-7 mainboards using 3.0-volt AGP graphics cards (3.0-volt AGP cards are not very common these days). Most new cards are 1.5-volt, and should pose no problem. The GeForce 3 Ti200 graphics card in my system does not pose any compatibility issues with the ALi chipset, although my older TNT2 card had a few issues on my motherboard (BCM VP-1541). They were all resolved by setting the AGP data rate to 1X. When I gave the card to my sister (Gigabyte GA-5AX, same chipset), she didn't seem to have any problems running it in 2X mode.
I hope this information helps. Just let me know if you have any more questions about either of these boards.