Some will tell you Dell, others will tell you Sony. From my view point, I think that they are right on par with each other in terms of build quality. If I were you, I'd go with whatever one offers the longest warranty, i.e. sometimes Dell will throw in an additional year for free.
The build quality is not the same. Dell's xps 13 is thinner and lighter. I own the VAIO CW and it has extra features like a quickboot os, and things like that. The dell studio xps 13 has a backlit keyboard, which the cw doesnt. The CW comes with better media software. It is not exactly 'the same.'