Crucial is a division of parent company Micron. They make memory modules using memory chips made by Micron (obviously).
As for PNY, they make decent quality memory modules, it just depends on the particular type of memory chips they happen to use. Corsair and Mushkin are in the same situation. All three make quality modules though, or they wouldn't back them by a lifetime warranty. You can usually judge the quality of most any product by the type of warranty the manufacturer offers. If they don't have faith in themselves, why should you? And no manufacturer will warrant their product for long if they know the product will not last as it is always in their favor to keep warranty costs to the absolute bare minimum.