^^^ Exactly you can rewire reason into cubase, that way you can use the class synths and samplers into cubase, and use some quality vsts for fx, mixing and production (as the ones in reason are a bit lame imho).
Which is better? neither, cubase is a proper sequencer host and is good for production and mixing, although the quality of the sounds depends on the vsts you use; reason is good because it allows you to put your ideas down quickly as its simple to use and all the basics building blocks are there ready for you to use.