For a few MMO I've played with Keyboard/mouse, its not too hard... but personally the character movement always felt so restricting.
Controller makes it much more free.
Altho I have to admit that most of the time keeping track of your cooldowns can be an issue since you will always have at most 16 buttons on view on the screen with the sole crosshotbar, so keyboard wins on that, as well as moving through menus, but I like the fact that I can hide EVERYTHING thanks to that too...

If you get used enough to the controller you can even play with the whole HUD hidden for a while and admire all the cool skill's light effects in a way you cant while staring at skills cooling down.
Since I play on PC with an Xbox controller, I think I can enjoy both features in a sense.

I would love that the camera spinning could be increased a 10 times fold tho...