This may not be 100% accurate so take it as grain of salt
From High to low order
Boxing
Increases your resistance to 23,077%
Boxing Passive
Learning boxing increases your Blocking/Parrying power by 10% regardless if it equiped or not, unknow if it stacks with shield
Iron leg
Increases your resistance to 26,489227%
Basic combat
Increases your resistance to 19,369787%
Sailor fist
Increases your resistance to 17,379%
Cannon Fist
Increases your resistance to 17,379%
Thermo Fist
Increases your resistance to 15,287245%
Intensity
Effect
Intensity increases your resistance, the high base resistance is, the more 1 point of intensity is worth.
Getting each point of intensity will decrease its effectiveness to prevent people from reaching too high