I've also asked this on GameFAQs, but I'd like to discuss it here, too.
The PS4 has:
Improved graphics, compared to a Wii U
Improved sound, compared to a Wii U
A better online system
Also, a Monster Hunter game for the PS4 would convince me to purchase a PS4 (the Monster Hunter game and The Order: 1886 would be just about all I need!)