I spent 15 years of my life fixing the "squealing brakes" issue on everything from Jags to Fords.
Cheap (Advance, Autozone, etc) rotors are junk. Even the big name guys like Napa and Triangle sell junk.
Most of the pads are junk.
Rotors and Pads should be bought as a set from a good supplier (Brembo, Toyota, EBC etc) The mix in the iron, and the compound in the friction materials are designed to work together (on quality shit anyway)
The squeal is the pad and rotor vibrating, thats why it's "light" braking that shows it the most.
The "anti squeal" pad is BS, it's putting "squish" in your brake system, and they still squeal.
After you install new, or cut rotors, or new or "sanded" pads, you need to "run them in".
Pad material needs to be "picked up" by the pores in the iron. Heat and friction does this. Run the car on a striaght road, and give the brakes a good smooth engagement, increasing pressure to about 80% of lockup over about 5 seconds.
Speed back up and do this agian 7 or 8 times , dont let the brakes cool down to much between engagements.
Back off, and do this with less and less pressure to bring the average temp down. Finally, you are just driving with "normal" braking.
Park it and let them cool off.
This will "run in " your new stuff and transfer pad material to the rotors evenly, and cook the "glue" off the pads.
When this is done right, the disk life is also extended, and you will get tons more stopping power.
NEVER SPRAY STUFF ON YOUR PADS OR ROTORS. (other than brake cleaner when you are installing)
I've fixed, god I cant count how many "problem" cars with this. Brembo makes brakes for just about everything, and their "oem replacement" rotors are awesome.
The "chamfer" deal is about pads that dont fit. If they are loose in the caliper, they will jump the hell around, etc. The chamfer keeps them from chattering, or helps, because the leading edge of the pad cant "buck" the rotor. (sort of like drums that are shot or out of adjustment)
If the factory pads had a chamfer, use chamfered pads. If not, it's just a "fix" to loose manufacturing tolerances.
Our toyotas came with fantastic brakes, the doped iron and pad mix is fantastic. I can out brake the "big brake" bitches with my stock stuff most of the time, because most of those guys just throw money at their shit, and have no idea what they are doing. They just want big shinny brakes.
Look at a race car, the rotors are not shinny. A superbike is another good example of quality stuff. They dont get shinny until you all but melt them off the bike, and then they turn a pretty gloss purple!
The cheapest best way to make the car stop, and right, is to just shell out the bucks to Toyota (or Brembo). They spent god knows how much money on R&D to get it right, and the Supra was never a "budget" car.
Fords on the other hand, make their rotors out of cheap crap. Thats why an F150 cant stop if you put more than a load of laundry in it. Might also be why they are hemorrhaging money from every orifice.