I suppose it depends on what you want to do with the laptop and what your expectations are. Overall, Macbook Pros are good laptops, with great build quality, but poor bang for the buck. If you want to use Mac OS, then you have no choice. The Dell XPS 15 is a high quality laptop and although it has a 15.6" screen, the thin bezels around the display mean the laptop is about equal to the size of a 14" laptop. If I am not mistaken, the battery life when doing average daily tasks is comparable to the MacBook Pro, roughly 8 hours.
If playing game is a concern, then go for the Dell because it has a GTX 1050. On the other hand, the Macbook relies on the Intel HD 640. Better than the typical Intel HD 620 / HD 630 found in Windows laptops, but not even close to the GTX 1050. The Mac has a dual core i5 or i7 CPU while the Dell has a quad core i7-7700HQ.
I would say that unless you really want to use Mac OS, the Dell is overall the better laptop.