While Titanfall is probably going to be the better game, the Xbox One will sell better in the US when Halo releases. With the release of Halo in 2014, I expect the Xbox One to overtake the PS4 in the US, but as much as Halo 4 sold at the end of the gen, once the PS4 starts coming out with more exclusives, US might be taken back over by PS4. I think US will be eventually taken over by PS4 but for atleast the first year might be between 45/50-50/50 in favor of Xbox One.
The Halo fanbase is pretty much 1/8.8 of the 360 sales. Those other users may or may not be swayed towards the PS4 being a more powerful and cheaper device.