I use a controller, as it is what I used in FFXI and 1.0 (so I'm just used to it), but as a bonus, it's easier on my RSI, and... I have small hands. Hitting the F1-F8 keys (or even the 1-5 keys) requires me to look down, move my hand, press the key, then look down again to move my hand back to WASD. Targeting on the controller, using the D-pad and targeting filters, is much easier and quicker for me, and because of the small hands issue, muscle memory for abilities works much better for me on the controller as well.
