Brake judder is caused by the disc rotor faces not running true to the pad material
There can be a few causes - some of which mentioned in the thread already
1) Warped discs - front discs can see often see 500deg C plus in a hard stop and the thermal stresses this sets up in the rotor can cause it to warp and become wavy. Hard stops and poor quality discs can increase the likelihood. Also as mentioned if you get the discs nice and hot and then clamp them by keeping you foot on the pedal you can distort the disc by clamping it while it cools
2) Hub face dirty. When the discs are bolted up to the hub, the assumption is that this face is true. Any dirt or corrosion on the face will cause the disc to have "run out" of true
3) Hub not true. If the front bearings have been badly replaced then this could cause run out
4) Caliper not sitting true - same reasons as the hub - dirt/corrosion on mountings - bit unlikely this as the pads should bed a bit to correct this.
Unless you driving style is really heavy on the brakes, or you are buying shonky discs, then it is odd this should happen 3 times to you. I would get a Dial Gauge rigged up, or ask your tech to do this, to measure the disc run out. Then check the hub face is clean and check it's run out too.
I hate to say it but OEM discs are usually a good bet - especially on fronts as they get a wee bit hot, so the additional quality is sometimes worth paying for if you are having problems.