WASD with shooters. but racing games for example for sure the arrow keys. but of course the best is a force feedback joystick controller for flight games!!
WSAD , Because i never used arrow keys :P its strange for me to use them. but its iritating because im used to hold my mouse in my left hand ... And my mouse has a Thumb placement ... but for the RIGHT hand ... so its iritating ( Yes i press WASD with my right hand)
it depend on the keys you use if you use the arows and you use left handed keys then arows would be good but if for example you play a run and gun were you left click most peaople would use their right hand to click so they would use the WASD keys