From Reddit, PVE Breakdown of Damage Resistance
Resilience is unfortunately not very useful in PVE aside from providing increased Barrier regen time for Titans. Each Tier of Resilience is effectively a 1-2% increase in overall shield, which ends up only being about a 0.5% increase in your overall resistance to damage.
At 15% resistance, and stacking up to a staggering 55.6%, it significantly outperforms other stackable mods. Most hard-hitting damage sources count as Area of Effect (AOE) damage and are reduced by this mod:
Concussive Blasts, Shots (This covers a lot of Bosses, Majors, Cyclops, Knights, and other sources)
Fire Pools, Grenades
Exploding Shanks, Screebs, Cursed Thralls
x1 - 15.00%
x2 - 27.75%
x3 - 38.59%
x4 - 47.80%
x5 - 55.63%
Arc, Solar, and Void Resist:
Unfortunately, elemental resists only provide a 5% resistance and stacks in a standard fashion
x1 - 5.00%
x2 - 9.75%
x3 - 14.26%
x4 - 18.55%
x5 - 22.62%
Minor, Major, and Boss Resist:
Minor, Major, and Boss Resist mods provide a stacking 10% resistance. However, this decreases in effectiveness faster than other mods. I would not recommend stacking more than 3 mods as this increase drops below even elemental resist.
x1 - 10.00%
x2 - 17.86%
x3 - 23.58%
x4 - 27.16%
x5 - 30.00%
Important note: For the purposes of Damage Resistance only, elite enemies with a Triangle Icon, including Champions, are actually considered Boss enemies. Use Boss Resist to decrease damage from them.
For Weapon Damage mods, you would use Major Spec to increase damage to Champions and other Elite enemies.
*Originally Posted by u/Bachmanetti on Reddit.
I suggest clicking the link above for a more thorough guide to damage resistance.