The majority of top games are on both and each has a nitch few exclusives that depending on what people like can sway them. Killzone is nice, but so is Halo and Titanfall. Both have racing games, FPS's, etc.. just different titles.
I think you could not go wrong with either one as a "gaming machine", but I give the overall advantage to the Xbox One as it is not just a video game console. Mom and pop type people can use it for skype, internet, NFL stuff, others can just play games so it covers a larger percentage of people.