It can go here too.

Typically, there is a damage type/several statuses missing from the level entirely. For instance, there is no fire/ice/shock/curse/sleep/poison in the jelly kingdom, nor is there any shadow defense. So the best thing defensively would be something like ironmight plate mail + volcanic plate helm, as these resist perfectly all damage types with a huge emphasis on the main damage type- normal, which is dealt by lumbers, minis, and slime cubes in varying but often high amounts.

So specializing in that damage type would be the best to go. However, status takes precedent above all else. Against vanaduke, the volcanic plate shield with its stun+fire resistance is better than the omega shell for that reason. The same goes for armor, provided that specialized defenses are a good fit for the threats on the level. For instance, +1 curse resistance doesn't do anything, but +5 curse resist gets you an extra weapon slot and +6 is overkill. Fire resistance is always worth something, but is worth a LOT more when you don't have any or have -2. Bringing chaos + divine veil + curse high battlesprite perk is a good fit when dealing with uFSC.

Here is what you need to know for statuses:
Whisps = +9
Curse = +5 (one weapon)
Fire resistance = stacks well with itself; can have a ton and it will do a ton
Ice resistance = almost worthless unless for whisps (except on shield)
Shock = stacks well with itself; can have a ton and it will do a ton
Poison = almost worthless unless EVERYWHERE; i.e. C42
Stun = Unpredictable, debatably worthwhile kind of
Sleep = Removed from game until further notice

The gist of this is that fire and shock are important and that ice and poison aren't, unless there are whisps everywhere in which case oh why not bring them. So for your first gear, you should get something that defends against fire and shock. Like the mask of seerus, or divine veil. If you want to play even more defensively, get two things that defend against both and put shock/fire UVs on them.

As for defenses, it is most important that you defend against what you'll take damage from. In FSC, vanaduke deals elemental+normal damage primarily. So using vog against him is better than fallen-- but fallen is better for the slags before him. If you're flawless against slags, bring vog. If you're flawless against vanaduke, bring fallen.

For a list of what does what damage type, see the wiki.

Good knights rarely get hit and only when they do does it really matter about defenses.

For example, I have been able to beat King of Ashes enough times to get a Fang of Vog and a Blackened crest even though the only 5star armor I bring is Mercurial mail.

That being said it is best to keep a varied and balanced array of armors as I would prefer my 3star angelic set over my Mercurial mail when dealing with Fiend levels.

This is a game of footwork and timing.

Before I joined Spiral knights I played another MMO Known as Realm of the mad god. In that game it is all about footwork as the more powerful monsters can kill you in just two of their rapid fire spread shots.