I have never stopped wearing the Hero of the Federation set because a 50% to avoid lethal damage with no internal cooldown is one of the most blatantly broken things I have seen in years. One time I was marked a traitor, I kept avoiding death while the bombardments were killing all the bugs chasing me. I could tell it was proc'ing a lot because I was spamming stims to regen health and for the speed boost but I was dropping to 1 hp constantly. Eventually I died but it completely turned a situation of us being overrun to a very manageable amount of bugs.
About the only armor skills I genuinely think is situational are
Servo Assisted and
Electrical Conduit - the former's sole purpose is allowing you to yeet strike beacons from ridiculous ranges, and if you don't need that, you will not be needing Servo Assisted. Limb damage resistance doesn't matter with how easy it is to heal and how easy it is to die in this game. Electrical Conduit meanwhile exists solely to enable the famed Ghostbusters Squad tactic: have everyone load up on Tesla towers, Blitzers, and Arc Throwers and any incidental damage you take is reduced to about 5% of what it does, taking basically all risk out of this. No arc damage means no reason to ever take it.
Fortified is excellent. The reduction in recoil is a big help to weapons that kick hard, and 50% reduction in explosive damage means you stand a good chance of surviving almost any incidental from the bots. That it's on so many good armors (including the "in between" Enforcer) is another plus.
Extra Padding is simple, but does the job. +50 Armor. Makes light armor as protective as medium, medium as heavy, heavy even tankier. Ideally, pair with vitality.
Med-Kit is deceptively strong and arguably among the best armor skills. +2 Stim Capacity is a big help and they last 2 seconds longer too. This can and will help you survive shit you have no business surviving, and uniquely among armor skills, the boost to your drugs also works on stimming your teammates. It also stacks with the new Booster so you can make your drugs even more ridiculous while getting more of them and making addicts out of your teammates.
Peak Physique is wonderful. You won't really notice the melee boost until you bring down medium enemies slightly faster, but the reduction in weapon sway and handling speed is absolutely incredible; try it with the Diligence Counter-Sniper or Dominator and you will see exactly what I mean; it is exceptionally strong.
Engineering Kit is Fortified's offensive cousin: Same reduction in recoil, but +2 grenades as opposed to 50% explosive resist. Engineering Kit is awesome when you're using Thermites or Impact Grenades and can be equally good when spamming Stuns which may in fact be the game's most broken throwable in the hands of a skilled player.
In terms of raw survivability,
Democracy Protects is hard to top. Torso damage, unlike limb damage, will lead to a bleed-out if not treated, and this skill prevents that. The ability to potentially never be one-shotted though leads to hilarious bullshit like players meleeing hellbombs to hurl themselves directly to the objective in seconds. It's absolutely awesome, but it only has a 1-in-2 chance to trigger and will only activate if you're over a certain health threshold; beware.
So you have two situational ones, a bunch of really good ones, and two outright hilariously bullshit ones. Good times.