The AMD chipsets, I believe, are hybrids. An AMD northbridge, and VIA 686b southbridge (there was a full AMD chipset, but I don't know if that's even available anymore). Your Abit KT7A also uses a 686b, along with a VIA KT-133a northbridge. VIA chips are known to be somewhat buggy. Especially the 686b southbridge. Data corruption, Creative SB Live problems, hardware incompatibilities, were among the common complaints. There were a lot of posts here regarding problems with VIA chipsets, and, more specifically, the 686b southbridge .
That being said, I've heard good things about VIA's 266a chipset (still, it <i>is</i> VIA!).
SIS's 735 chip(set) has gotten good reviews. There have been a number of posts regarding ECS's 735 solution, but I think that's more an ECS problem than a chip(set) problem.
The ALi MaGiK 1 chipset is also quite stable, though it's getting dated at this point. I hear there's a new revision out (or coming out soon), that's <i>supposed</i> to be on par with the performance of the 266a chipset. But that's mere speculation.
NVIDIA's NForce mobo specs have been impressive, but I don't think it's available quite yet (should be soon). We'll have to wait and see what the final retail version will offer in terms of performance and stability. I think the reviews of the NForce reference boards have been quite positive overall.
Just my 2 cents...