I had this problem with a worn front right balljoint. It could easily be a suspension component, that when put under the load of braking (disc brakes exerting localised force right next to the balljoint), it causes shaking. It could also be warped rotors (especially if they are EBC), not very likely though unless you spend most of your time braking hard from high speed and then leaving your foot on the brakes at stop lights.
I only had the shaking when braking, and the new ball joint sorted it. So it's possibly not the brakes. Jack up the front wheels one at a time, and check for excessive play. If it's tight when you rock the wheel from side to side with your hands, the balljoint is fine, not sure how to check for other suspension component failures though.
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