I've done both and like my Razer Onza corded XBox 360 controller. It has these extra shoulder bumpers I can set to Back/Start.

If you go with keyboard/mouse, make sure to set aside an few hours for customizing. The default keys are all spread out and the hot keys get crappy. Also, the click boxes for targets can be non-intuitive and I found it a bit obnoxious.

The biggest draw back for the controller, to me, is there is no "Use Items" binding. During soloing, I often have to reach for the U key so I can pop a potion mid-battle. If they'd just let me swap out my Status Effect binding with Use Items, I'd turn on the "Chat Keyboard" option and never touch it again.

Some Keyboard advice:

First off, unbind A and D from walk left/walk right and Q and E from strafe left/right.

A -> Strafe Left
D -> Strafe Right
Q -> Main Menu
E -> Something else you do a lot (Like moving Chat off Space Bar)

I believe R, F, and D default to some targeting functions. If you feel they're excessive, drop one and use it for "Use Item".

The rest is up to you, but I *strongly* recommend the rearrangement to get the Main Menu binding to Q. Otherwise you'll find yourself spending an annoyingly big portion of your playing time reaching across to the Home key.