The XBO will probably win august. Last years august was pretty darn close, thanks to the Madden bundle, and this year the price is at 349$, and in addition to the Madden bundle, they also have Gears Ultimate and Rare Replay. Now of course, the september PS4 bundles will also siphon PS4 sales (just like the Destiny bundle did last year), but the PS4 also has Until Dawn.
2014 august:
XBO - Madden bundle, promotions, 399$ base price
PS4 - Nothing (except multiplats ofc), 399$ base price, september bundles stealing sales
~20k gap in PS4s favour iirc
2015 august
XBO - Madden bundle, promotions, 349$ base price, Gears Ultimate, Rare Replay.
PS4 - Until Dawn, 399$ base price, september bundles siphoning sales.
=XBO win