Considering "equal and opposite reactions" and "conservation of momentum" concepts... here a science book (though not necessarily a practical) answer to the question "which has least recoil."
If one defines recoil as the amount of energy or momentum imparted to your hand by the gun, then for a given 9mm round, shortest-barreled 9mm pistols (< 3") should technically "recoil" least. Less barrel length = less distance the bullet is pushed = less energy (Force x Distance) imparted to the bullet. The longer barrels should generate more bullet energy and hence more recoil energy.
The equal and opposite reaction of the bullet's motion is imparted to the gun.
The mass of a heavier gun slows the guns rearward motion.
The slower motion backward subsequently generates a lower force to the hands over a longer time. Springs can also reduce and spread the reaction force over time.
Practically, heavier guns with long barrels are perceived to have "softer" recoil,
Short-barreled guns both lighter weight and incorporate stiffer recoil springs.
This means the short-barreled guns move back faster and impart higher force,
which are perceived as harsher.
So the recoil from a longer/heavier gun is perceived to be a lower "kick" when your hand has actually absorbed both more energy and momentum.
FWIW.
If one defines recoil as the amount of energy or momentum imparted to your hand by the gun, then for a given 9mm round, shortest-barreled 9mm pistols (< 3") should technically "recoil" least. Less barrel length = less distance the bullet is pushed = less energy (Force x Distance) imparted to the bullet. The longer barrels should generate more bullet energy and hence more recoil energy.
The equal and opposite reaction of the bullet's motion is imparted to the gun.
The mass of a heavier gun slows the guns rearward motion.
The slower motion backward subsequently generates a lower force to the hands over a longer time. Springs can also reduce and spread the reaction force over time.
Practically, heavier guns with long barrels are perceived to have "softer" recoil,
Short-barreled guns both lighter weight and incorporate stiffer recoil springs.
This means the short-barreled guns move back faster and impart higher force,
which are perceived as harsher.
So the recoil from a longer/heavier gun is perceived to be a lower "kick" when your hand has actually absorbed both more energy and momentum.
FWIW.