In all honesty, both sides have still yet to prove they can deliver anything this gen. They have some 5 years to work their magic, since both have announced that until 2022 their plan is to deliver crossgen games.
Also, forget about last gen, it was more thanks to Nintendo and Xbox shooting their own foot than about Sony's competence.
Nintendo on the other hand, has the userbase, has the games, and has the lowest price for entry.
Nintendo's success is already guaranteed, but Xbox and Sony have yet to do something this gen.