PS4 without a doubt. Although there may be an argument that the Wii U might have the higher attach rate in terms of percentage, by the time the game arrives there is likely to be well over 3:1 in terms of PS4 over Wii U in customers hands. So for sales numbers, the PS4 wins by default.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M