Don't listen to any of these jackasses who act like there's only one right answer. It all comes down to personal preference, just like with sticks vs pads. What I can say for sure, though, is that the PS4 seems to have better converter-less, alternative fightpad options.
I've owned quite a few fightpads in my day and have a preference for 6-button ones, though not as vehemently for MK/Injustice as SF/Marvel. My latest acquisition was the Hori FC, which was pretty cheap at just $40 on Amazon, and I'm definitely a fan so far except for the fact that I wish the sides came down a bit further to give me more to grip. I know the FC4 has exactly that going for it so I might have been better off with that one, but I heard their were rotating dpad issues and I'm sure I'll get used to the way this one fits my hand soon enough anyway.
Before that for about two weeks I had what was ALLEGEDLY supposed to be the new Madcatz SFV pad with the FIXED d-pad, and as aesthetically dope as it was, diagonal up-forward just stopped working. So that's a pass on that shit, which is a shame because Madcatz actually finally got it right before that with - of all pads believe it or not - their WWE Brawlpads. That was my go-to for injustice on my 360 and still a contender for my all time favorite.
I've also got an Elite controller on the XB1 and it honestly isn't that much of an improvement over the standard controller at all for fighters, but the standard pad isn't too horrible either for MK. It still left me wanting more though and without a converter I just don't think I'd find it on XB1.
TL;DR: See how the DS4 feels and know you've got options if you don't like it. Hori pads seem like the way to go if you're planning on playing SF too or any other games that favor a 6 button layout, though.
