A quick rundown of fun quirks to lock on class

[Panfilo]

This is just a basic rundown, personal tastes will vary.

Universally good quirks:
On Guard: +4 speed, +5 dodge on first turn, too good to pass up. Excellent on everybody.
Quickdraw: The same, minus the dodge, also great for the speed.
Quick Reflexes: Speed is life, never hurts to have more.
Warrior of Light: Benefits both melee and ranged, and stacks with other damage bonuses.
Natural Swing: A universal ACC benefit is very good at Champion difficulty vs high dodge targets.

Leper, Man at Arms: Tough, Hard Skinned, Evasive.
Both these heroes are tanky heroes, with ways to draw fire to themselves. So having more health, prot, and dodge adds up, particularly for the Man at Arms. Alternatively, you can lock in one of the +5ACC quirks in lieu of evasive which benefits the Leper.

Hellion, Abomination: Warrior of Light, Slugger, Precise Striker.
+20% more damage and 3% more crit would be an amazing trinket in of itself, and when stacked with other damage and/or speed trinkets allows you to explode enemies before they can act. Both these heroes are fast enough to generally go before their foes, and being able to frontload more damage can make a big difference, especially in Apprentice/Veteran dungeons. But even in Champion, extra damage is useful vs 'damage race' bosses.

Abomination: Steady, Resilent
An alternative build for Abomination is to give him -10% stress taken and +10% stress received, to offset the stress buildup and help him bring his stress down faster. This combo is also helpful for an Occultist whose camp skills stress him out.

Occultist: Eldrich Slayer, Eldrich Hater, On Guard/Quickdraw
The name of the game here is having an Occultist who can get huge stacked bonuses vs Eldrich, by taking Etherial Crucifix and either Eldrich killing Incense or Eldrich Slaying Ring, park in the 3rd position and stab/artillery eldrich targets to death for huge crits. When stacked up, at Apprentice/Veteran you can OHKO the back two rows in Cove runs with him. A specialist, but a very powerful one useful in both Cove and some of the final stages of the game.

Bounty Hunter: Man Slayer, Man Hater, Precise Striker[/b]
A similar type of specialist as the Occultist, this build makes the Bounty Hunter extremely powerful vs human targets. The advantage here is that human encounters can happen in any dungeon, so it will always be potentially relevant, but really shine in the Wolves at the Door event.

Houndmaster: Beast Slayer, Beast Hater, Eagle Eye[/b]
A similar type of specialist, this one useful in the Warrens and Weald. While Hound's Rush by itself isn't spectacular, the bonuses it gets to Beasts, marked, along with the CC set bonus and dog treats can make that dog hit like a truck.

Arbalest, Grave Robber: Eagle Eye, Deadly, Unerring
Maximizing ranged damage allows both these heroes to bust out huge crits on their targets. Both already benefit from shooting at marked targets, allowing you to kill big tough enemies considerably faster. The Grave Robber in particular can OHKO an annoying, fast back row stress dealer before they can even act with a nice crit. And good crit streaks also stress heal your party,

Flagellant: Last Gasp, Second Wind, and either Slugger or Quick Reflexes.
the Flagellant is unique in that he is the most effective when under 50% health, making these situational quirks actually helpful for him. In the most dire of situations, he's the most likely to act first, which gives you the chance to use either of his amazing self-heal abilities when you need it most.