Let me preface this by saying I realize this is just an opinion, and also that I considered the Xbox 360 controller to be the best controller of all time. I had both PS3 and Xbox 360 last gen, the PS3 mostly collected dust, and besides the fact most of my friends/fam are on Xbox, part of my 360 bias had to do with the fact that the controller was LEAGUES better than the Dualshock 3.
Fast forward, in this one gamer's opinion the One controller is WORSE than the 360, almost ruined. It doesn't fit my hand as well, although I cannot pinpoint why, it just isn't as comfortable. I keep accidentally pressing in on the left aim trigger in FPS, not sure if the placement changed or they made it more sensitive. This happens at least once but usually multiple times per match.
The placement of the shoulder buttons is also a big step back. They're just not easy to hit moving from the triggers, too high and/or far back? It just doesn't feel natural. The menu and options or whatever they call the Start and Select buttons now, also hard to find, and for my tastes, although the verdict is still out on this, I don't like the new analog sticks, although they look cool, they're a bit too small and it's tougher to keep them in constant contact with your thumb. Not sure if it's the fact that the controller doesn't seem to fit my hand overall as well anymore, but my aim is not as good as it is on 360 or even PS4 (I own both).
I never thought this was possible after last gen, but I actually think the Dualshock 4 is better than the Xbox One controller. DS4 so much better than DS3, the triggers and buttons are placed well, the sticks seem to be just the right size and easy to keep contact with, the touchpad seems unnecessary but is actually really helpful in COD for pulling up the score quickly since the button is so big. It's just a comfortable controller that works well.
I am NOT a fanboy. I own both systems, and truthfully if I had to only have 1 I would HANDS down pick the Xbox One. I love all the multimedia and multitasking functions, putting my TV through it, and I love Xbox Fitness and Kinect. I was playing a game and watching an NBA game on TV at the same time which was awesome. And as I said earlier most of my friends/fam are on XBL. But I am dissapointed in the controller, IMO they sorta ruined the best controller of all time.
Kudos on the new D-Pad, and the new guide button, and getting rid of the battery bulge, but overall a step back.