The SiS745 is hardly anything of an improvement over the SiS735 (just as the KT333 is barely improved over the KT266A). It only adds support for Firewire (not even implemented in the ECS K7S6A) and DDR333 support.
I'd wait for KT333A and SiS746. Both are due out shortly after KT333 and SiS745 and they both feature ATA133, AGP8x, USB 2.0, and Firewire (the first three not available natively with either 745 or KT333).
As for ECS's quality, no where near something like Asus or Gigabyte.