Titanfall is not an Xbox 1 exclusive, they've already announced that it will be released for both the PC and the 360.
It won't be released on the PS4 at the same time as the Xbox 1, 360, and PC, but the developers have said that they would like release the game on the PS4 as well.
So yeah, it'll probably be out for the PS4 within a year or so.
I see no reason to buy it anywhere but PC myself. The Xbox 1 version will likely be the next best thing, but 360 owners who don't jump right onboard for the new platform will also get to play a version of the game.