For quick, rapid, turns in which I need to sprint immediately in the other direction, I use my mouse. This is used in avoiding AoE effects, getting somewhere quickly, or rotating my direction of my character to ensure that my back is not turned to anything and that I am facing the right direction to hit mobs while rapidly changing mobs while AoE tanking.
For slow, gradual turns, used in kiting or the positioning of a mob, I use the A and D keys.
For moving forwards and backwards consistently without needing to stop immediately, I use W and S to go forward or back, and Q and E for strafing left and right. If I want to start and stop repeatedly, I hold down both my mouse buttons and release them when I want to stop.