I think an MPEG4 video can be .avi or .asf (and probably other formats too). Having had cameras that take both .asf and .avi, I haven't developed a preference. Which means that compared to the image quality, whether the files are .asf or .avi isn't important.
Same as cmos or ccd sensors. They have different characteristics, but overall they seem to do equally well as implemented in these cameras.