You know, this is an amazingly good question, and I fancy writing a question that I know full well, noone will ever read. If it's a game where I'm using the mouse to shoot as well, I will opt for WASD but if I'm using other keys, eg. space, I would definitely opt for the arrow keys. Thank you for allowing me to perform this rant.
1. it is far away from other keys that are quite unfortunate when pressed, like caps
2. i often scroll down a page with the arrows instead of the sidebar or mouse roller thing.seems alot easier to me.
3. whenever i use wasd, i ALWAYS ( /exaggeration) manage to srew it up, like ill be pressing f instead of d or vice versa. it is near impossible to do this with the arrows. as a result of this mismatch, i am often hurt or lose the level while playing a game.
I don't have problems with WASD but unless nessesary I perfer to use the Arrow keys, even when I use them with a left hand(I just move the keyboard left)