It's so difficult to predict the Switch right now, with how little we know of the upcoming support through to the end of the year.
With the PlayStation 4 we know what's on the horizon (Final Fantasy 7, The Last of Us, God of War, Red Dead, Spiderman and a Major Pricecut), but with the Switch they could drop any number of major titles. We already know it has a bunch of smaller titles in Yoshi and Kirby coming to go along with Dragon Quest, but after that Nintendo have been fairly quiet. Smash Bros? 2D Mario? Animal Crossing? Could Pokémon be ready for the end of 2018?!
Hmm.
PS4 - 19 Million
Switch - 17 Million
Xbox One - 8 Million
3DS - 3 Million
A healthy year for the industry. PS4 edges it thanks to the $199 cut late on.