Vray seems to be more memory efficient (which I believe is a known thing). I can throw a giant scene at vray with 100's of lights, 1000's of proxies (some massive in disk size also), and insane Revit model(s) and it'll render fast, and not complain, whereas corona will start to give me memory warnings and tell me the rendering will come out with dark spots or somesuch. To be honest this has only happened on one very complex project, however it has informed my decision on which engine to use for which type of project. This is (just one of the reasons) why I still use both renderers.