On dry pavement the front brake does most of the stopping, because weight transfers forward under braking. So for a quick stop you generally want both brakes, with a smooth squeeze on the front and the rear used to stabilize.
I don’t really think in terms of “which first” — I feather the rear, then progressively load the front. In low traction (wet/gravel) you use less front and keep everything smooth to avoid lockups. Rear-first as a habit can mean longer stopping distances, but grabbing front too hard is what sends people over the bars.
Rule of thumb: both brakes, smooth + progressive, adjust front/rear bias to conditions.