I find that I have much more control over my toon with WASD. I can then CHOOSE if I want to follow my opponent, move to the left, right, etc. It's been reported by beta users in this game that their position relative to the enemy can affect the percentage of accuracy and damage recieved/dealt. With click to move you can't really be as finely accurate with what angle/position you want to attack from.
People have different preferences. I've played with both styles and I enjoy WASD a bit more. Especially when I have this bad boy. I can Macro WASD to the D-Pad and the Hotkeys @ my fingertips. ;D
Belkin : Nostromo SpeedPad n52