Are you looking for a console just to play MKX? Or are you looking for a console to game on across the board. Depending on your answer, you could go either way, really you could go either way regardless.
For MKX, the PS4 is the offline tournament standard, but right now the online ESL tournaments will only be on Xbox One (no word if there will be a PS4 ESL tournament coming for Season 2). So depending on if you are trying to get into the offline scene, or wanting to play in the online ESL scene, you can go either way. If you don't care about tournaments, either system should meet your needs.
If you are looking for a console just to game on in general, that is different thing, and far more subjective if you ask me.
Both consoles have their ups and downs. The biggest things I see are that the PS4 generally has higher res games as PS4 is the leading dev platform and generally the stronger console (graphics chip wise), but Xbox One has the better backend software with the Cloud, backwards compatibility, and the frequent updates for stability and more features/services.
So yeah, it depends on what you want. This holiday the Xbox will have the edge in games as it will get all the 3rd party stuff that PS4 is getting, plus MS's own exclusives. To contrast with the PS4, this holiday for Sony is sparse as the only AAA exclusive coming out is Uncharted 4 early next year (iirc). If you want to play good new games this holiday, plus you like MS's staple franchises and games that have already been released, get the Xbox One. If you like Sony's franchises, the games that have already been release, and can wait until later next year for the other big games to drop, then get a PS4.
