Under controlled trials on dry pavement, the fastest stops were done using only the front brake. My guess at the reason for that result is that one is only concentrating on one lever instead of two and of course the rear brake is not doing anything when braking at the limit with the front.
There's gotta be someone here who's been around long enough to remember the video of the ultimate braking job. A racer descending at high speed sees a hairpin ahead of him on which several riders have just crashed. Team cars are stopped on the hairpin, probably giving aid.. He hits the front brake hard, bringing the rear wheel 6"-12" off the ground and holds that pose until he finally crashes into one of the cars blocking the hairpin. Perfect braking and bike handling, too bad that wasn't enough.
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Results matter