Naturally, WASD puts left-handers who use their left hand to control the mouse and right hand to control the keyboard, at a disadvantage. Do you use your left hand to control your mouse?
I'm right handed so using the mouse and such I like to use my right hand, so using the arrow keys especially on a laptop become really awkward. So overall I'm going with WASD
This is a hard choice because Wasd keys are better for games like side scrolling shooters that require you to reload(R key), and switch between weapons (numbers or Q & E). For example Raze or The Last Stand's.
The Arrow keys are for platforming games or racing type platformers that only require movement. For example Exit Path, or the Platform Racing's.
But over all, I would have to go with the arrow keys, just because I am right handed and I don't know, easier to control with my right hand. Plus I am on a desktop, now if I had a laptop, I might choose Wasd.