Not sure exactly, but I have noticed some brakes are definitely worse than others - perhaps uneven wear on the left vs right causing different amounts of heat build up.
The 737-800 has the worst brakes out of any Boeing I've flown - can be quite difficult to apply evenly and without dancing down the runway, especially with moderate application.
I tend to leave the auto brakes in as long as possible for this reason - much smoother application. My pet peeve is the heavy braking to make a rapid exit instead of taking an extra minute to taxi back to the bay.