In most of what I read, it says there's no quality difference between CAV & CLV and I believe in most cases that is probably true.
I always felt CAV looked a lot better. I seem to remember that blacks (i.e., the black bars around a widescreen movie) were much blacker with CAV, whereas CLV would introduce some blue speckling. I assume it's because CAV allows more bits (about double, in total, though it varies from the beginning to the end of a CAV side) for digitising the composite video signal.
DE