I perfer keyboard and mouse to play FFIXV

Having played with both, I perfer keyboard and mouse hand over fist.
That having been said, using a controller is intuitive, straight forward, easy and quick. There is no detriment outside of socialization with the controller taken a little time to adjust.
Oh, and they altered quest handins with the keyboard and mouse, right click the slot for the quest hand in, it'll pop up

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the item that goes there.

Personally I hate keyboard/mouse. I mean, I DO play on laptop so I must plug in my mouse, however I also must plug in my controller so it's no big deal.

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Personally I just find fighting, movement... pretty much everything except precise targeting and chatting much more easier with a controller. It's really down to your own personal style.

At the moment I even really have more of a hybrid set-up...much of my HUD I control with my touchpad however I actually play the game with my controller. (And, obviously, I chat with my keyboard.)

While I do think the targeting could use a bit of....adjustments... it's not enough to make me switch back to using only keyboard/mouse. If I'm really in a pinch and for some reason the controller has wigged out and won't give me my target I need, I just reach over and mouse select it like a lazy bum. Whatever.